unsmob_pitch -> Pitch::unsmob and related

unsmob_pitch -> Pitch::unsmob and related

This is part of moving away from implementing LilyPond infrastructure
via the C preprocessor rather than C++ features since C++ features tend
to be more transparent to IDEs, debuggers, editors, and newcomers.

sed -i "$(git grep -h DECLARE_UNSMOB|sed 's/.*(\(.*\), \(.*\)).*/s\/unsmob_\2\\b\/\1::unsmob\/g/')" $(git grep -l unsmob_)
sed -i '/^DECLARE_UNSMOB/d' `git grep -l DECLARE_UNSMOB`
git checkout Documentation/misc/CHANGES-1.3

(the changes to the CHANGES file are not useful).

The definition of DECLARE_UNSMOB is removed in a separate commit.