To build FluidSynth API reference documentation, make sure you have Doxygen
installed.

If you are using the cmake build system, change to the root build directory.
If you are using the deprecated auto-tools based build system, execute the 
following command in this doc/ directory:

$ make doxygen

The latest generated API HTML docs can also be found, along with other
information, on the Wiki documentation page:
http://sourceforge.net/apps/trac/fluidsynth/wiki/Documentation