Run scripts : added 'yd' as the game folder.
Data : added four OBJ models under yd/pieces folder.  These will be used
in the experimental code for loading TMX files into Darkplaces.
Engine : added empty 'model_tmx.c' code file, will contain code for
loading the TMX map format used by the Tiled map editor.
Engine : bit more work on TMX loader -- copied most of the OBJ loading
code (excising the actual parsing stuff).  As a "do nothing" loader it
is working very well ;)
Data : enable developer and sv_cheats in default.cfg
TMX : test crud for setting 'brush.entities' to something (using that
instead of a ".ent" file).  It worked.
Removed the testing map (test.obj + test.ent)