despawn: fix negative coordinate bug,  real_coordinates: refactor, map: provide definitive absolutes for real_coordinates

despawn_monsters: correct inaccuracies at negative coordinates via
real_coordinates: refactored to return correct subdivisions for any coordinate, when provided absolute coordinates
map: provide absolute xy for map xy, via point getabs(mx, my).
map: Provide local xy for absolute with point getlocal(ax, ay)
map: Provide local and absolute inbound checks via bool inbounds(mx, my) and bool inboundsabs(ax, ay)
map: record submap x,y,z for grid[0] in 'abs_sub' and 'worldz' via set_abs_sub() on load/shift
overmap: show overmap and overmap point coordinates of cursor