SNDINFO Support Implemented

Rudimentary Hexen-compliance-level implementation of SNDINFO has been completed for sound effects. Still TODO is respecting map music specifications set through this lump.

Note that EE supports a special $EDFOVERRIDE keyword in SNDINFO. Sounds defined through SNDINFO cannot override sounds defined by EDF unless this keyword appears in the same lump with the definitions. This is for compatibility with cross-port mods which intentionally provide different data in an EDFROOT or ESNDINFO lump for EE and a SNDINFO lump for ZDoom.

I have requested that the ZDoom team add the ability to ignore this keyword in their SNDINFO parser.