Add a luac linter for Lua

test/handler/test_luac_handler.vader

@@ -0,0 +1,36 @@
+Before:
+  Save g:ale_warn_about_trailing_whitespace
+
+  let g:ale_warn_about_trailing_whitespace = 1
+
+  runtime ale_linters/lua/luac.vim
+
+After:
+  Restore
+  call ale#linter#Reset()
+
+Execute(The luac handler should parse lines correctly):
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 1,
+  \     'text': 'line contains trailing whitespace',
+  \     'type': 'E',
+  \   },
+  \   {
+  \     'lnum': 3,
+  \     'text': 'unexpected symbol near ''-''',
+  \     'type': 'E',
+  \   },
+  \   {
+  \     'lnum': 5,
+  \     'text': '''='' expected near '')''',
+  \     'type': 'E',
+  \   },
+  \ ],
+  \ ale_linters#lua#luac#Handle(347, [
+  \   'luac /file/path/here.lua:1: line contains trailing whitespace',
+  \   'luac /file/path/here.lua:3: unexpected symbol near ''-''',
+  \   'luac /file/path/here.lua:5: ''='' expected near '')''',
+  \ ])
+