Truncate long sequence and transpose to different keys in pianoroll dataset creation. (#757)
Truncate long sequence and transpose to different keys in pianoroll dataset creation. (#757)

* Truncate instead of discarding long sequences

* Transpose inputs for pianoroll model

* Transpose inputs for pianoroll model

* Transpose inputs for pianoroll model

* Accidental change

* Make max_steps_discard and *_truncate mutually exclusive.

* lint

* lint

magenta/note-seq,magenta/note-seq,magenta/note-seq