Implement saving SEQ files

+ Add editor control for SEQ files
+ Add unimplemented SEQ.Load
Add argument validation to Crash
Add argument validation to Crash.Audio
Fix a SEQ constructor exception message
Add argument validation to Crash.Graphics
Change VAB to VH in music entries
Write a function for reading/writing 3-byte data (for tempo)

+ Add Crash.Audio.MIDIConv
+ Use MIDIConv.To3BE and MIDIConv.From3BE