Add support for Lua files

[pdesaulniers]

Right now, the extension only checks .tl files. It could also check .lua files in 'lax' mode.

[pdesaulniers]

For the time being, I think luacheck is more useful than tl at verifying plain Lua code.

Once teal-language/tl#89 is implemented, we might be able to use tl check as a luacheck replacement.

[tommitytom]

Just a note, that this is excellent for general lua programming: https://marketplace.visualstudio.com/items?itemName=sumneko.lua

[pdesaulniers]

You're right, it's very good! I was still using https://github.com/trixnz/vscode-lua, which is much less feature-rich...

[tommitytom]

A further note on the previously mentioned extension, this is an interesting development:

https://github.com/sumneko/lua-language-server/wiki/Annotations
https://github.com/sumneko/lua-language-server/wiki/Plugins

[dipyalov]

It seems like tree-sitter-teal grammar doesn't support lua files and generates wrong tokens, so intellisense won't work correctly