Added phpstan linter for php. (#772)

* Added phpstan linter for php.

ale_linters/php/phpstan.vim

@@ -0,0 +1,40 @@
+" Author: medains <https://github.com/medains>, ardis <https://github.com/ardisdreelath>
+" Description: phpstan for PHP files
+
+" Set to change the ruleset
+let g:ale_php_phpstan_executable = get(g:, 'ale_php_phpstan_executable', 'phpstan')
+let g:ale_php_phpstan_level = get(g:, 'ale_php_phpstan_level', '4')
+
+function! ale_linters#php#phpstan#GetCommand(buffer) abort
+    return ale#Var(a:buffer, 'php_phpstan_executable')
+    \   . ' analyze -l'
+    \   . ale#Var(a:buffer, 'php_phpstan_level')
+    \   . ' --errorFormat raw'
+    \   . ' %s'
+endfunction
+
+function! ale_linters#php#phpstan#Handle(buffer, lines) abort
+    " Matches against lines like the following:
+    "
+    " filename.php:15:message
+    " C:\folder\filename.php:15:message
+    let l:pattern = '^\([a-zA-Z]:\)\?[^:]\+:\(\d\+\):\(.*\)$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        call add(l:output, {
+        \   'lnum': l:match[2] + 0,
+        \   'text': l:match[3],
+        \   'type': 'W',
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('php', {
+\   'name': 'phpstan',
+\   'executable': 'phpstan',
+\   'command_callback': 'ale_linters#php#phpstan#GetCommand',
+\   'callback': 'ale_linters#php#phpstan#Handle',
+\})