Documentation|API|libdeng2: Macro expanding when running Doxygen
Fixed|Music: Expand symbols in the soundfont path
Cherry picked fc533afe4576f13aeac4d5b8e9e31c8bc89a1c72
Documentation|API: Tweaked Doxygen config

Something is not working quite right with Doxygen's macro expansion.
Fixed|libdeng2: Incorrect return type for fequal

Also added a single-precision version of the function.
Merge branch 'master' into ui-framework