More fixes to enemy render

Fixed enemies rendering 180deg different than expected, minimap
adjustments.

atan2 is used to find angle of ray from player to enemy, return value
was 180deg out of phase of player.direction baseline reference. By
always subtracting Math.PI from atan2 return before comparison with
player.direction, angle deltas were calculated correctly.

Still need to adjust the left and top render points of enemies, and
scaling. At the moment renders like missiles do, and can appear a full
gridpoint left than true position. Ultimately need to move away from
lazy render towards a true z ordered column drawing.

Adjusted minimap render to show player direction, draw entities smaller
than walls, and added a general map boundary to constrain entities to.