Added 'dpdefs' top-level folder, containing QC definitions for Darkplaces
(copied from Darkplaces 2013-03-04 source code).
Menu : updated progs.src for top-level dpdefs/
Run-linux.sh : check for an installed binary of 'darkplaces', run it if found.
Also fixed name of other one to --> bin/darkplaces-linux-686-sdl
.gitignore
Have a top-level 'Makefile' for building all QC programs.
(this replaces menu/Makefile).
Makefile : added rules to build the game and client QC programs (though
we don't have any code for them yet....)
README.md : note the top-level Makefile