fix hint and gl2 build. NOTE: this does not change that GL2 segfaults right away. that is an issue that dates back at least 50 commits, but most likely even back to the webgl merge. I guess nobody actually tried to run hedgewars in GL2 since back then :P
uWorld does not require uMatrix anymore
tiny lua documentation fix
fix possible engine crash that a lua script could cause by passing an invalid geartype to addgear
WIP: PlaceSprite for lua API.  also changed PlaceGirder so that it will return true/false for whether placing was successful too
make enums crash-safe. and other fixes