Sound IDs equated

Equated sound IDs and applied them to every appropriate area I could
find. The Sound Flag slots were missing a number of equates ($E2, $E3,).
I equated some IDs that already had available constants, but weren't
modified to use them for whatever reason. There are too many non-equated
instances to list here.

Pointed out sound driver slot allocation bugs with attached fixes under
Sound_ChkValue.

Corrected LevSel_NoCheat's comments and expanded on the nature of a
group of instructions.
Changed Go_SoundD0 to Go_SpecSoundIndex

This is a part of making the special SFXes look less like a cheap hack
made just for $D0, and more of its own system, as it actually is. It
just happens to be occupied by only one sound, and its index just
happens to be underneath the normal SFXes index.
Added more 'music' and 'sfx' macros

I don't care for these, but there were some appropriate places for them
to be used.
Merge pull request #3 from Clownacy/master

Sound IDs equated