transpose: support all combinations of numbers and strings for notes and intervals

[felixroos]

this all works now:

note("40 40 40").transpose("0 1 2"); // "40 41 42"
"40 40 40".transpose("0 1 2"); // "40 41 42"
note("40 40 40").transpose("1P 2M 3m"); // "40 42 43"
"40 40 40".transpose("1P 2M 3m"); // "40 42 43"
note("c c c").transpose("0 1 2"); // "C Db D"
"c c c".transpose("0 1 2"); // "C Db D"
note("c c c").transpose("1P 2M 3m"); // "C D Eb"
"c c c".transpose("1P 2M 3m"); // "C D Eb"

this makes .transpose a drop-in replacement for .add, because the syntax note(...).add(...) was removed in #1026, so it can now be replaced with note(...).transpose(...)