Tree-sitter integration on feature/tree-sitter

[Yuan Fu]

Guys,

I’ve pushed the tree-sitter integration to feature/tree-sitter. If anyone want 
to give it a try:
- get tree-sitter from GitHub (or your package manager, make sure the version 
is at least 0.20.2)
https://github.com/tree-sitter/tree-sitter
- pull and build the branch
- read (elisp)Parsing Program Source
- grab language definitions from https://github.com/casouri/tree-sitter-module
You can either build with my script, or download the prebuilt ones
- play with it

Also apologize in advance for that my response might be slow until like June :-)

Yuan