== Handles
As a general pattern, these libraries have an interface based on integer
handles allocated by Open() and released by Close(); in the AliceSoft's
implementation, handles are pointers to internal objects. Note that:
* 0 is used to represent an invalid handle, and
* Small numbers cannot be handles. For example, Mamanyonyo has code that
treats an integer as a CG number if it is less than 10000, and as a
surface handle otherwise.
In this patch, handles are generated using id_pool.h functions. In order
to achieve the above, the interface is extended so that the minimum ID
value can be specified (the `base` parameter of id_pool_init()).
== Graphics System
Surface objects (implemented in vmSurface.[ch]) plays a central role in
Mamanyonyo's graphics system, and the sprite system (vmSprite.c) is
implemented on top of it. vmSprite.c uses scene.h functions.
== vmChrLoader and vmMapLoader
Since Mamanyonyo's character data format is the same as Widenyo's,
the ChrLoader code has been refactored and used from vmChrLoader.c.
On the other hand, MapLoader and vmMapLoader do not share code because
the map file format is different from Widenyo.
Replace SDL_mixer with an audio implementation using libsndfile,
sts_mixer (a single-file header library) and SDL's basic audio
interface.
This allows for much more flexibility in controlling audio playback.
Fading is now properly implemented, as well as various other functions
from the SACT2/KiwiSoundEngine interface.
sts_mixer can support recursive mixing, so it will be possible to
implement the "VolumeValancer" mixer channels specified in
System40.ini in the future (once I figure out how the mapping of audio
files to mixer channels is supposed to work).
kichikuou