Upgrade to mistletoe-ebp 0.9.4a2

Update to `mistletoe-ebp==0.9.4a2` dependency (#110)

This update allows us to drop most of the span token patching code, and we now use the `Math` token directly from mistletoe.

It also improves how token sets are instantiated within the renderers, making it a lot easier to swap in/out tokens to be included in the parse.

Upgrade to `mistletoe-ebp~=0.9.2`

mistletoe-ebp v0.9 introduces a major API improvement, particularly for block tokens (how they are parsed/stored) and capture of source positions. This allows the majority of the code in myst_parser/block_tokens.py to be removed, in favour of the upstream implementations.

Breaking changes:

• range field renamed to position
• ASTRenderer renamed to JsonRenderer
• FrontMatter is stored as an attribute of Document (rather than a child)
• source text is now parsed by Document.read(text), instead of Document(text) (@choldgraf this will need to be changed in MyST-NB)

Fix RTD Deployment

v0.3.2

Fix RTD deployment

Initial PyPi release

Move to `mistletoe-ebp` dependency (#107)

* Move pandas_sphinx_theme requirement to separate file

Its current form is not accepted by pypi (awaiting pypi release of this package)

* Add PyPi distribution and documentation

* bump version

Intial release for alpha testing

v0.3.0

Reference `master` as the default branch (#105)