Introduce generic unix formatter

Two wrapper functions allow treating lines as errors or as warnings

ale_linters/go/govet.vim

@@ -7,40 +7,11 @@ endif
 
 let g:loaded_ale_linters_go_govet = 1
 
-function! ale_linters#go#govet#Handle(buffer, lines)
-    " Matches patterns line the following:
-    "
-    " file.go:27: missing argument for Printf("%s"): format reads arg 2, have only 1 args
-    let l:pattern = '^.*:\(\d\+\): \(.\+\)$'
-    let l:output = []
-
-    for l:line in a:lines
-        let l:match = matchlist(l:line, l:pattern)
-
-        if len(l:match) == 0
-            continue
-        endif
-
-        " vcol is Needed to indicate that the column is a character.
-        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('go', {
 \   'name': 'go vet',
 \   'output_stream': 'stderr',
 \   'executable': 'go',
 \   'command': g:ale#util#stdin_wrapper . ' .go go vet',
-\   'callback': 'ale_linters#go#govet#Handle',
+\   'callback': 'ale#handlers#HandleUnixFormatAsError',
 \})