Quite often the user wants to experiment what particular unit(s) add
to the sound. This commit adds ability to disable any set of units
temporarily, without actually deleting them. Ctrl-D disables and
re-enables the units. Disabled units are considered non-existent in
the patch.
Closes#116.
The commands and values were not very good names to what the
byte sequences actually are: opcodes and their operands. In
many other places, we were already calling the byte in the Command
stream as Opcode, so a logical name for a sequence of these is
Opcodes. Values is such a generic name that it's not immediately
clear that this sequence is related to the opcodes. Operands is not
perfect but clearly suggests that this sequence is related to
the Opcodes.
