New linter: dls (#1992)

* New linter: dls

autoload/ale/d.vim

@@ -0,0 +1,16 @@
+" Author: Auri <me@aurieh.me>
+" Description: Functions for integrating with D linters.
+
+function! ale#d#FindDUBConfig(buffer) abort
+    " Find a DUB configuration file in ancestor paths.
+    " The most DUB-specific names will be tried first.
+    for l:possible_filename in ['dub.sdl', 'dub.json', 'package.json']
+        let l:dub_file = ale#path#FindNearestFile(a:buffer, l:possible_filename)
+
+        if !empty(l:dub_file)
+            return l:dub_file
+        endif
+    endfor
+
+    return ''
+endfunction