Added hack linter for php (#239)

* added hack linter

* updated docs for hack (hh_client)

* naming

ale_linters/php/hack.vim

@@ -0,0 +1,37 @@
+" Author: Zefei Xuan <https://github.com/zefei>
+" Description: Hack type checking (http://hacklang.org/)
+
+function! ale_linters#php#hack#Handle(buffer, lines)
+    let l:pattern = '^\(.*\):\(\d\+\):\(\d\+\),\(\d\+\): \(.\+])\)$'
+    let l:output = []
+
+    for l:line in a:lines
+        let l:match = matchlist(l:line, l:pattern)
+
+        if len(l:match) == 0
+            continue
+        endif
+
+        if a:buffer != bufnr(l:match[1])
+          continue
+        endif
+
+        call add(l:output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': l:match[2] + 0,
+        \   'vcol': 0,
+        \   'col': l:match[3] + 0,
+        \   'text': l:match[5],
+        \   'type': 'E',
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('php', {
+\   'name': 'hack',
+\   'executable': 'hh_client',
+\   'command': 'hh_client --retries 0 --retry-if-init false',
+\   'callback': 'ale_linters#php#hack#Handle',
+\})