Pass parameter by const ref instead of const value.
Remove unneeded explicit keyword.
Pass parameter by const ref instead of const value.
Return const references instead of const objects.
Use Doxygen comment.
Use private members instead of protected members.
Use const const_iterators instead of iterator.
ExpAI: make recruiting work with all keys of [chance_to_hit] special

Previously there would be an error, and subsequently no recruiting, if
the value= key was not set.
Fix some spelling mistakes in comments.
Fix spelling in a comment.
Fix spelling.
Fix the spelling in comments.
Fix the spelling in comments.
Remove a duplicate command.
Added mini-map specific buttons.
Remove an old style cast.
Mark system headers as system headers in CMake.

Compilers suppress some errors in system headers, this avoids false
positives of some compiler warnings not in our source code.
Fix spelling in a comment.
Hotkey for the minimap team&movement/side color coding feature.
Wired in a button for the minimap color coding.