Fixed crash when --track or --kart is used and no default player exists.
Also only print an error message if --track or --kart do not work (e.g.
the track/kart is not unlocked, or no default player exists) instead of
aborting STK.
Added more comments.
Ignore doxygen output files in src/html.
Merge branch 'master' of github.com:supertuxkart/stk-code