Adding key signatures to generated chorales

[napulen]

This PR adds key signatures to the generated chorales.

Currently, the generated score shows the accidentals in every note, and has a key signature of C / a:

It'd be better to output the key signature that corresponds to the key of the chorale:

Some artifacts are still happening with the accidentals. For example, the first B- shouldn't be printed. I am afraid that has to do with how music21 processes the score. Yet, I still think it would be good to add this change here, and maybe submit an issue in music21 related to the artifacts in accidentals. Maybe there is a more idiomatic way of encoding the chorales in music21 that works better with their routines for generating the score.

[ekzhang]

Yeah, good point, I've had issues in the past re: key signatures as well. It seems like Music21 handles this somewhat inconsistently. I'll try to take a look.

[napulen]

My guess is that it has to do with the intermediate Measure objects that music21 adds to the representation. In many files I have parsed with music21, I remember I seeing the key signatures encoded at the beginning of Measure0 or Measure1.

I like your encoding strategy, because it separates the voices across the 2 staffs and its super compact code-wise. However, it doesn't have any measures and I imagined these are constructed automatically by music21 at some point. Maybe the library is struggling during that process, and having the intermediate Measure objects would fix this issue.

I still think this looks more like a music21 bug, maybe. I think it's logical to encode the notes/time signature and expect the library to handle the rest automatically.