Refactor GoatGUIEngine into various files under src/parts/.
The external interface to this code is the functions prefixed with PE_
and generally following the naming of the HLL functions which they
implement.
The reason for this is that there are multiple HLL libraries that
implement more or less the same GUI interface (GoatGUIEngine, GUIEngine
and PartsEngine).
Also added here are a number of miscellaneous stubbed-out HLL functions
that are used by Rance 01 (which now runs up to the point where it tries
to create the title menu).
Nunuhara Cabbage