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.