LaTeX Linters (#190)

* Add chktex linter

* Alias plaintex to tex

* Add lacheck linter

Closes #179

* Add the chktex warning code

This very useful to have when you want to suppress lint warnings with LaTeX
comments. chktex tends to be a bit noisy so this often needed.

* lacheck: Make regex less specific

To be more robust future changes in `stdin-wrapper`

autoload/ale/linter.vim

@@ -9,6 +9,7 @@ let s:linters = {}
 let s:default_ale_linter_aliases = {
 \   'zsh': 'sh',
 \   'csh': 'sh',
+\   'plaintex': 'tex'
 \}
 
 " Default linters to run for particular filetypes.