Move the sasslint handlers to one location

autoload/ale/handlers/sasslint.vim

@@ -0,0 +1,8 @@
+" Author: KabbAmine - https://github.com/KabbAmine,
+"   Ben Falconer <ben@falconers.me.uk>
+
+function! ale#handlers#sasslint#GetCommand(buffer) abort
+    return ale#path#BufferCdString(a:buffer)
+    \   . ale#Escape('sass-lint')
+    \   . ' -v -q -f compact %t'
+endfunction