Drop the enumerated pitch values.

It's really just as easy to use macros such as PITCH_LITERAL,
PITCH_NAME, or PITCH_ACCIDENTAL in some combination instead of using
an enumerated pitch_t value.

In place of the enum, we now have pitch_t as a uint32_t type.

The real purpose for doing this is to prepare for pitch_t to be able
to hold the octave as well which should be remarkably convenient.