Jtools

Major updates include more tests and aligning more closely with the JavaScript version of this
project: https://github.com/BlendingJake/JTools-JS

* Add `===` and `!==` to match the strict equality checking needed in the JS version.
The methods `seq` and `sne` have been added to `Key` to correspond with the new filters. `===` is the same as `==` and `!==` in the same as `!=` in the Python version.

* Rename `null` -> `!present` and `!null` -> `present`. Corresponding methods have been renamed
to `not_present` and `present`. This filter will catch values that are `null` or `undefined`.

* Make membership filters (`in`, `contains`, `!in` and `!contains`) work properly with
strings, lists, dicts, and sets.

* Remove `$datetime`. See below for replacement.

* Add `$call` and `$attr` for calling a function and accessing an attribute. Can be used to replace
`$datetime` functionality.

* Remove `Formatter.format` and add `Formatter.single` and `Formatter.many` to be consistent across
other classes and support formatting arrays of items.

* Add more tests to increase coverage and do basic performance testing

* Query strings can now start with specials to allow operations on the entire object being passed.
* Bug fixes and more unit tests

* Added new specials, mostly relating to time
* `$parse_timestamp`
* `$datetime`
* `$strptime`
* `$strftime`
* Added `not` filtering and the `interval` and `!interval` operators
* Made `Filter` consistent with `Getter` by removing `.filter()` and adding
`.single()` and `.many()`
* Added `fallback` to `Getter`
* added numerous unit tests

* Rename `Getter.get` to `Getter.single`
* Add `Getter.many`
* Support getting multiple fields at once by changing `Getter` to allow `Getter(<field>)` and `Getter([<field>, <field>, ...])`
* Change `Filter`'s before for when there are no filters. Now, by default, all items will be returned unless `Filter(..., empty_filters_response=False)`

* add three new specials: `$not`, `$ternary(if_true, if_false, strict=False)`, and `$strip`. The first two are intended to help with handling booleans, the other strips whitespace off of strings
* added in some tests and test data
* update docs, documenting new features and correcting some basic mistakes