A Preprocessor takes a token from the Staccato string, does some computation on the string,
and returns the String results of the computation so it may be included back into the
Staccato string. This is used for functionality that can be expressed in a String but must
be expanded to actual Staccato instructions.
The MicrotonePreprocess is an example of this. The user is allowed to express a microtone
using 'm' followed by the frequency - e.g., m440. The MicrotonePreprocessor takes this String,
parses the frequency value, figures out what Pitch Wheel and Note events need to be called to
generate this frequency in MIDI, and returns the full set of Staccato Pitch Wheel and Note