Update grammar for tree-sitter

[kylebarron]

A new style of language grammar will be available with Atom 1.25, called tree-sitter. This seems to be more advanced than the current system, first-mate.

It looks like the new syntax is currently documented here:
https://github.com/tree-sitter/tree-sitter/blob/master/doc/grammar-schema.json

[kylebarron]

This is an example of the new python grammar for tree-sitter.

[guillaumechaumet]

Nice Kyle. It seems more readable than the previous one. I will look at it. Thanks

[guillaumechaumet]

https://github.com/REditorSupport/atom-language-r/blob/master/grammars/tree-sitter-r.cson