Add SQL linter sqlint, closes #395 (#472)

ale_linters/sql/sqlint.vim

@@ -0,0 +1,34 @@
+" Author: Adriaan Zonnenberg <amz@adriaan.xyz>
+" Description: sqlint for SQL files
+
+function! ale_linters#sql#sqlint#Handle(buffer, lines) abort
+    " Matches patterns like the following:
+    "
+    " stdin:3:1:ERROR syntax error at or near "WIBBLE"
+    let l:pattern = '\v^[^:]+:(\d+):(\d+):(\u+) (.*)'
+    let l:output = []
+
+    for l:line in a:lines
+        let l:match = matchlist(l:line, l:pattern)
+
+        if empty(l:match)
+            continue
+        endif
+
+        call add(l:output, {
+        \   'lnum': l:match[1] + 0,
+        \   'col': l:match[2] + 0,
+        \   'type': l:match[3][0],
+        \   'text': l:match[4],
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('sql', {
+\   'name': 'sqlint',
+\   'executable': 'sqlint',
+\   'command': 'sqlint',
+\   'callback': 'ale_linters#sql#sqlint#Handle',
+\})