improve readme
Make it possible to have a unit without shadow, and not have it crashing
by checking for NULL and then not copying.
on second thought, let the copy function allow null and return null back
(be graceful with null)
Update readme with requirements of this feature
remove devastator.bmp because it should not be in root
only instantiate move behavior classes once, and use them in all units
where needed.
add requirement
add 5 soldiers, with coordinates as if the sub-cells already exist, just
to give some sense of how it looks like
communicate clearly that the x,y coordinates are world-coordinates
because I get confused every time
introduce a concept of sub-positioning units
introduce foot move behavior and attach it to the soldier unit type so
it has no concept of occupied cells and therefor seems to move perfectly
plot units with map x,y coordinates using repository.
add 5 more soldiers
update feature tasks list
remove sub_position as it makes everything more complex. Instead draw on
position.
add development flag which enables grid to be drawn so I can see how
units are drawn in respect to their cells which I need to know if I want
to get foot based unit positioned correctly on a single cell
- this breaks moving behavior for now
- there is no concept anymore of a sub-cell
- all units are positioned at the 'position' point which is from now on
  regarded as the center of a unit
- drawing has been fixed to respect 'position' to be center of unit
- units can have a different size opposed to the tile size, although it
  is not really used yet. This is needed for infantry which has tiles of
  32x32px but the units themselves are ~ 8x8px and they all should be
  able to be placed on the same 32x32px cell.
- add DEV compiler flags to show target of unit, next move position and
  the current position. Later one is needed to know how the unit was
  being drawn in respect to the actual position
fixes drawing of lines in DEV mode for unit, so it actually draws from
the position and not the coordinate used for blitting
add comments to explain offset_x, offset_y
update readme
snap coordinates, at center of cell, which fixes movement (back-forth
movement) for units which occupy the whole cell. This does not fix
movement for foot-units.