Shifted player 2's spawn point to be symmetrical with that of player 1.  Fixed player 2's initial facing direction and initial dx.  The 'RESPAWN' debug input now also resets both player's initial spawn points as well as their initial dx.
Monster spawn points are no longer drawn as red boxes unless debug view is on.
Monsters are now one of several colors, picked at random when spawned.  Changed the 'KILLALL' debug input to set every monster's hp to 0 instead of just clearing the 'active_monsters' list.
Starting to deal with monsters dropping skills when killed and players picking up these dropped skills.
Moved skill box creation to within 'GameLoop.__init__._setup_skill_boxes'.  Skill ids for each skill box and player is now displayed in the skill boxes.
Changed possible colors for monsters, debug 'RESPAWN' input now also resets initial facing direction.
Fixed merge conflicts.
Merge branch 'mk13-master'
Minor changes to 'Arena' class, minor code formatting.
More minor code formatting.
The 'q' key no longer exits the game; use 'esc' instead.
Changed mouse debug font color, changed spawn points for arena3, minor code formatting.
Better handling of error when loading sprite image.
(1)-Added 'kind' to 'monster_info_nt' / 'MONSTER_TABLE' / 'Monster'.  (2)-Dropped skills are no longer included when iterating through Arena objects.  (3)-Added 'draw_dropped_skills' which draws dropped skills as well as the skill id number on the dropped skill rect.  (4)-Added a few basic functions within skills.py to help getting appropriate skills to drop.