Add grammars module

[lapp0]

Fixes #543

Rendered docs: https://github.com/lapp0/outlines/blob/cfg-examples/docs/quickstart.md#built-in-grammars

Makes it easy to add grammars to the module, define a lark file in outlines/lark, reference it in grammars.py.

Work

• allow grammar Path to be passed to CFGFSM and reference outlines/lark as lark importables
• Introduce grammars.py and minimal example, outlines.grammars.json
• test outlines.grammars.json with CFGFSM
• Add to docs
• Awaiting Fix incompleteness of regex and cfg guided generation #544 merge

Out of scope

• Fixing escaped_string per Handle regexps with lookaround #456
• Adding SQL, Python, etc grammars

[rlouf]

I think we could rename outlines.lark to outlines.grammars? Otherwise this requires user to know what lark is and add cognitive overhead.

[rlouf]

Now that #544 has been merged you will need to rebase your brain on main and fix the merge conflicts. It would also be nice to have some documentation :) This can go in the "Utiltities" section under "Docs".

[rlouf]

Good to merge, thank you!