First pass of audio ucodes refactoring.

I've reworked my code for audio ucodes and tried to organize my commits more logically.

What I've completed:
-ucode version/revision detection (not iplementation)
-most basic audio commands are refactored
-code that is shared between alist based ucode are in alist.c / alist_internal.h
-code that is shared between alist based ucode and musy ucode is in audio.c / audio.h
-READABILITY ;) yeah

What I've left for later:
-ucodemp3 -> this is a huge beast and deserve a separate treatment
-envmixers commands -> there are many subtleties and possible way to screw this (arithmetic, differences between versions, ...) so I left it for later
-most of ucode2 specific commands
-version/revision subtleties implementation
-Improvements like POLEF, SEGMENT, COPYBLOCKS, ... (they will come, don't worry)

All of this should allow better understanding of what is going on and be a solid base to improve further.