Parce

- don't (yet) use positional-only arguments, keep python 3.6 support
- simplified LilyPond tokenizing, removed identifier context

- simplified LilyPond language definition, many improvements
- rule.findmember now creates one dict under the hood which is faster
- fixed deadlock when a rule in a lexicon derived the same lexicon
- Lexicon.arg is now readonly (a Lexicon should be a immutable).

- fix a treebuilder bug where different derived lexicons compared the same
- here documents in bash are supported, other bash improvements
- improvements to lilypond lexing
- improvements to util.Dispatcher: tread safe and more powerful
- more editor style properties were added to the themes
- added pastel and solarized light and dark themes
- improved terminal theme colors
- small indenting fixes
- added tests/themes.html to view the themes in a browser
- added examples page to the docs, using the examples from the tests/ dir.
- many documentation updates

- fixed treebuilder.build_tree() function with root lexicon None
- fixed multiple selectors in css prelude not working
- fixed small formatting glitches with multi-theme formatter
- Formatter can now handle _unparsed class, added debug theme
- more colors in default theme
- language examples in documentation are now rendered with parce
- added chapter about syntax highlighting to documentation
- many parce classes now have prettier repr
- added Bash and C languages

- redesigned theme and formatter module
- HtmlFormatter is now usable and documented
- fixed first ±10 tokens marked as updated even if they didn't change
- added Tcl and DocBook languages
- many documentation updates and improvements

- documentation switched to Furo theme, looks better on small devices
- the rule item MATCH(n) has changed to MATCH[n], which is more uniform
- the rule item char() has been renamed to chars()
- regex.to_string() now supports named Unicode literals
- fixed transformation of escaped text in Json
- util.Switch can now be used as class instance, as descriptor
- added methods to indent.Indenter to auto_indent, increase or decrease indent
- added Document.append() to append text at the end