New feature: Cache grammars for fast initialization of Lark

This is straight-forward, and such a feature already exists in PLY, for example. This would be especially beneficial for LALR.

It should be fairly easy to write, since the Lark class already supports serialization and deserialization. All that’s required is to add an interface for saving/loading it to some temporary file.

[MegaIng]

It would be important to include the lark version inside the hash to make sure that lark doesn’t try to load an incompatible parser.

[erezsh]

Another set of values is also possible, and perhaps preferable:

• cache=False will disable cache

• cache=True (default) will use a temporary file selected by Lark, based on hash

• cache=“filename” will use that path for saving the file, still considering hash to prevent versioning issues (Also accepts Path objects).

Do you think the first is better, or this one?