Merged the functionality from each games' p_sound.c/h into common source files in libcommon.
Reworked sector sound start interface, splitting the plane origin selection out of P_SectorSound() and into the new function named P_PlaneSound(). Behavior is unchanged, i.e., playing a sound from a plane origin via this interface will automatically stop sounds playing from other origins in the same sector.
libcommon|Refactor: Commonized map sound interface
Merged the functionality from each games' p_sound.c/h into common
source files in libcommon.
Reworked sector sound start interface, splitting the plane origin
selection out of P_SectorSound() and into the new function named
P_PlaneSound(). Behavior is unchanged, i.e., playing a sound from
a plane origin via this interface will automatically stop sounds
playing from other origins in the same sector.