Add a new SCORE_PITCH macro and rename SCORE_PITCH_VALUE to SCORE_PITCH_LITERAL

Add a new SCORE_PITCH macro and rename SCORE_PITCH_VALUE to SCORE_PITCH_LITERAL

The original SCORE_PITCH_VALUE macro was of limited use. It could only
be used with literal values such as "G" and "FLAT" and could not be
used to construct a score_pitch_t value from two variables. This was
particularly useless since a user could just use a literal value of
SCORE_PITCH_Gf instead of SCORE_PITCH_VALUE(G, FLAT).

So we rename SCORE_PITCH_VALUE to SCORE_PITCH_LITERAL to make its
limitations more clear in its name. (The one important use remaining
for the macro is in the initial construction of the score_pitch_t
values for the enum declaration).

And here we add the SCORE_PITCH macro which *can* be used to construct
a score_pitch_t value from two variables, (one holding the pitch name,
and one holding the accidental).