feat/refacto: improve configurations

- You should now get the configs through functions
- Configs for languages are now inside a local object called parsers
- You can get the parser installation configurations with `get_parser_configs`
- A new object has been initialized inside configs to specify module config (called config).
- Provide functions to enable/disable a module on one buffer
- Provide functions to enable/disable a module on all buffers, and if filetype is
  specified, for specific filetype
- Provide function to determine if module is activated for a specified filetype

plugin/nvim-treesitter.vim

@@ -4,14 +4,17 @@ if exists('g:loaded_nvim_treesitter')
   finish
 endif
 
-lua << EOF
-ts_installable_parsers = function()
-  return table.concat(require'nvim-treesitter'.available_parsers(), '\n')
-end
-require'nvim-treesitter'._root.setup()
-EOF
+augroup NvimTreesitter
+augroup END
 
 let g:loaded_nvim_treesitter = 1
 
-augroup NvimTreesitter
-augroup END
+lua << EOF
+ts_installable_parsers = function()
+  return table.concat(require'nvim-treesitter.configs'.available_parsers(), '\n')
+end
+ts_available_modules = function()
+  return table.concat(require'nvim-treesitter.configs'.available_modules(), '\n')
+end
+require'nvim-treesitter'.setup()
+EOF