What's Changed

• Refactor in loaders -> Musa. Now notes are not grouped in instruments or bars but they are referenced to them with attributes.
• Build beats and subbeats objects when loading a MIDI file with the Musa class in laoders.
• Support tempo and time signature changes.
• Refactor pianoroll plots to support multi-track plotting.

What's New

• REMI tokenizer (with thempo and time signature changes).
• Chord detection algorithm at beat-level.
• Add graph representation of symbolic music (features module).