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`

ale_linters/tex/lacheck.vim

@@ -0,0 +1,50 @@
+" Author: Andrew Balmos - <andrew@balmos.org>
+" Description: lacheck for LaTeX files
+
+let g:ale_tex_lacheck_executable =
+\   get(g:, 'ale_tex_lacheck_executable', 'lacheck')
+
+function! ale_linters#tex#lacheck#Handle(buffer, lines) abort
+  " Mattes lines like:
+  "
+  " "book.tex", line 37: possible unwanted space at "{"
+  " "book.tex", line 38: missing `\ ' after "etc."
+
+  let l:pattern = '^".\+", line \(\d\+\): \(.\+\)$'
+  let l:output = []
+
+  for l:line in a:lines
+    let l:match = matchlist(l:line, l:pattern)
+
+    if len(l:match) == 0
+      continue
+    endif
+
+    " lacheck follows `\input{}` commands. If the cwd is not the same as the
+    " file in the buffer then it will fail to find the inputed items. We do not
+    " want warnings from those items anyway
+    if !empty(matchstr(l:match[2], '^Could not open ".\+"$'))
+      continue
+    endif
+
+    call add(l:output, {
+    \   'bufnr': a:buffer,
+    \   'lnum': l:match[1] + 0,
+    \   'vcol': 0,
+    \   'col': 0,
+    \   'text': l:match[2],
+    \   'type': 'W',
+    \   'nr': -1
+    \})
+  endfor
+
+  return l:output
+endfunction
+
+call ale#linter#Define('tex', {
+\   'name': 'lacheck',
+\   'executable': 'lacheck',
+\   'command': g:ale#util#stdin_wrapper . ' .tex '
+\      . g:ale_tex_lacheck_executable,
+\   'callback': 'ale_linters#tex#lacheck#Handle'
+\})