Pregex

- Added classes "pregex.meta.essentials.{Text, NonWhitespace, Whitespace}".

- Class "pregex.core.groups.Group" and method "pregex.core.pre.Pregex.group"
now have an "is_case_insensitive" parameter, which can be used in order to
apply the "case insenitive" modifier to the pattern that is wrapped within
the group.

- A "CannotBeNegatedException" is now thrown whenever one attempts to
invert an instance of class "pregex.core.classes.Any".

- Fixed bug where subtracting a character from a two-character class
range wouldn't successfully remove said character from the range.

- Slightly updated documentation and README.

- Modified some existing tests and added some more in order to achieve 100% coverage.

- Introducing the concept of "Extensibility": All patterns that correspond to classes within "pregex.meta" have numerous assertions imposed upon them, that are essential in order for them to be able to match what they are supposed to. These assertions are mostly word boundaries that are placed at the start and at the end of the pattern, but there might be other types of assertions as well. Helpful as they are for matching, these assertions might complicate things when it comes to the pattern being used as a building block to a larger pattern. For that reason, there has been added an "is_extensible" parameter to the constructor of every meta class. As a general rule of thumb, you should only set "is_extensible" to "True" if you wish to use a pattern as part of a larger one. For matching purposes, let "is_extensible" take its default value of "False".

- Class "pregex.core.pre.Pregex" now contains a set of "{get, iterate}_named_captures" methods through which one has access to any named captured groups stored within dictionaries.

- Parameter "pattern" of class "pregex.core.pre.Pregex" constructor now defaults to the empty string, thus replacing "pregex.core.pre.Empty" which has now been removed.

- All classes within "pregex.core.operators" can now receive one or even no arguments at all without throwing a "NotEnoughArgumentsException" exception. This makes it easier to do stuff like "pre = op.Either(*patterns)" without having to check whether list "patterns" contains more than one pattern.

- Applying the alternation operator between a pattern "P" and the empty string pattern now results in pattern "P" itself.

- Wrapping the empty string pattern in either a capturing or a non-capturing group now results into the empty string pattern itself.

- Classes "pregex.core.assertions.{__PositiveLookaround, __NegativeLookaround}" have been removed and replaced by a single class "pregex.core.assertions.__Lookaround".

- Classes "pregex.core.assertions.{FollowedBy, PrecededBy, EnclosedBy}" are now able to receive more than one assertion patterns, just like their negative counterparts.

- Class "pregex.meta.essentials.Date" now receives date formats in a list instead of as arbitrary arguments.

- Corrected mistake where method "pregex.core.pre.Pregex.not_enclosed_by" could receive multiple arguments.

- Updated documentaton and README.

- Modified some existing tests and added some more.

- Updated documentaton.
- Added pattern chaining (see Documentation/Covering the Basics/Pattern chaining).
- "pregex.core.groups.Backreference" can now receive integers besides strings in order to reference capturing groups by order, e.g. "\1", "\2", etc...
- "pregex.core.operators.Enclose" can now receive multiple "enclosing" patterns.
- Wrapping the empty string pattern within a group is now allowed.
- Alternating between a pattern and the empty string pattern is now allowed.
- Added params "capture_local_part" and "capture_domain" to "essentials.Email".
- Renamed "CannotBeQuantifiedException" to "CannotBeRepeatedException".
- Renamed private field "Pregex.__quantifiable" to "__repeatable".
- Renamed protected method "Pregex._is_quantifiable" to "Pregex._is_repeatable".
- Modified some existing tests and added some more.

- Split pregex package into "pregex.core" and "pregex.meta". All previous modules were moved to "pregex.core", while a new module "essentials.py" was added to "pregex.meta".
- Greatly improved documentation page.
- Added classes "pregex.core.assertions.[Not]EnclosedBy".
- Added "Pregex.print_pattern()" method just for printing the pattern.
- Added "Pregex.purge()" static method for clearing the regex cache.
- Added "__quantifiable" field and "_is_quantifiable" method.
- All match-like methods are now able to receive a path to a text file to extract text from in order to look for matches, via the "is_path" parameter.
- "Pregex.__infer_type" now also infers whether pattern is quantifiable or not, and returns said result along with the pattern's type.

- Updated docs and README.
- Replaced "pregex.assertions.MatchAt[Left|Right]WordBoundary" classes with single class "pregex.assertions.WordBoundary".
- Added class "pregex.assertions.NonWordBoundary".
- Added type "pregex.pre._Type.Empty".
- Added class "pregex.pre._Empty".
- Multiplying a "Pregex" instance with zero now returns the "Empty" pattern.
- Parameter value n=0 is now allowed in "pregex.quantifiers.Exactly" and returns the "Empty" pattern.
- Parameter combination (min, max) = (0, 0) in "pregex.quantifiers.AtLeastAtMost" is now alloed and returns "Empty" pattern.
- Removed private method "pregex.__add".
- Removed unused "type: _Type" parameter from "pregex.operators.__Operator".
- Split "pregex.assertions.__Lookaround" to "__PositiveLookaround" and "__NegativeLookaround".
- Negative lookarounds are now able to receive more than one pattern restrictions.
- Added "pregex.exceptions.ZeroArgumentsException".
- Classes "pregex.classes.Any[But]From" now throw an exception if provided with zero parameters.
- Fixed bug in "Pregex.__infer_type" method.
- Slightly modified some exceptions' messages.
- Modified existing tests and added some more.

- Updated README file and docs.
- Added a "CONTRIBUTING.md" file.
- Fixed a bug occuring whenever applying "Concat/Either" on more than two patterns.
- Fixed a bug occuring whenever multiplying an "__Assertion" class instance with an integer.
- Added unicode flag "u" to string returned by "Pregex.get_pattern" when "include_flags"
- Renamed "Pregex.iter_capturing_groups[_and_pos]" to "Pregex.iter_captures[_and_pos]". is set to "True".
- Renamed "Pregex.get_capturing_groups[_and_pos]" to "Pregex.get_captures[_and_pos]".
- Renamed "Pregex.split_by_group" to "Pregex.split_by_capture".
- Added parameter "is_global" to "AnyWordChar" and "AnyButWordChar".
- Added "GlobalWordCharException" that is thrown whenever one tries to subtract from "AnyWordChar/AnyButWordChar" where "include_foreign_chars" has been set to "True".
- Added a number of new classes in "tokens.py" for matching useful symbols.
- Added a number of new classes in "classes.py" for matching foreign characters.
- Fixed bug in "Any[But]From" resulting in these classes being able to accept non-tokens as parameters.
- Renamed "Any[But]WithinRange" to "Any[But]Between".
- Loosened restrictions on what constitutes a range in "AnyBetween/AnyButBetween".
- Modified existing tests for all the above and added some new ones.