Changes
/* Set Volume Envelope */ Bit 7 is for hw/sw envelope
In: A=Envelope number (1..15), HL=Pointer to Data (must be >3FFFh)
The data block starts with a header byte:
The following 3-byte parameters can be (when Byte 0, Bit7=0):
Byte 0 Number of steps (01h..7Fh)
