DUB: link to local library

[rcor via Digitalmars-d-learn]

Finally got it:
{
   "name": "test",
   "importPaths": ["ext/dallegro5"],
   "lflags": ["-Lext/dallegro5"],
   "libs": [
     "allegro",
     "allegro_acodec",
     "allegro_audio",
     "allegro_font",
     "allegro_ttf",
     "allegro_image",
     "allegro_color",
     "allegro_primitives"
   ],
   "dependencies": {
     "dallegro5": "~master"
   }
}

I had to specify the C libs for allegro and its addons.
Also, specifying dallegro5 as a dependency does seem to be 
necessary (this is after adding with `dub add local`).
Thanks for all the suggestions.