vm.Synth was used only in a few places, reduce the number of
exported functions. Also, if we ever add some global configuration
to GoSynther e.g. samplerate, we have a mechanism to do so, instead
of the Synth function.
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.
The -er suffix is more idiomatic for single method interfaces, and
the interface is not doing much more than converting the patch to a
synth. Names were updated throughout the project to reflect this
change. In particular, the "Service" in SynthService was not telling
anything helpful.
