Fixed point accumulation error. Still exist a problem with a text that doesnt disappear after one game ends and a new starts.
Replaced flags with coin animation. Introduced toxic gas in gui.
Added sound to poison. Changed flag to coin everywhere. Updated all file headers in tank_engine.
Removed vehicle comments from tank_engine, and also removed ACE-stuff from the CmakeList.
Merge branch 'master' into engine-flags
Transfer of negative points

When a player gets points below zero, they are transferred to the
opponent instead to keep the minimun score to zero.
Code cleanup
Improved printouts

Added player names to the printouts to make them more readable