Game : added INV_DecodeSpawnParms(), INV_EncodeSpawnParms() and
INV_InitialSpawnParms() functions to inventory.qc
Game : moved Player_Jump() and Player_Obituary() code --> player.qc,
and removed the WaterJump() stuff.
Game : moved SV_ParseClientCommand() --> client.qc
Game / world.qc : removed unused main() crud.
Game : added a 'null_entity' global, an more readable alias for 'world'.
Game : added new qc file 'game.qc', currently empty, which will be
responsible for important game state and non-client callbacks.
Game : moved 'StartFrame()' function --> game.qc, and added empty EndFrame()
and SV_Shutdown() functions.
Client : added 'dpdefs/keycodes.qc' to client progs.src
Client : implemented TAB key (via +button8) as "free camera" mode, holding
it down allows player to look around with the mouse (turning off the cursor).

A minor annoyance is that when releasing TAB, the pointer returns to the
wrong position (the center of the screen).

A _MAJOR_ annoyance is that binding this to a mouse button does not work
properly, pressing it once works, but next button down event does nothing,
then next one works, etc....  Seems the problem is in SDL library, as the
SDL_MOUSEBUTTONDOWN event is not received.