Add multi tracks

[cainky]

Description

This pull request introduces the feature of supporting multiple tracks in the MidiGen library. This feature is crucial for composers and developers looking to create more intricate MIDI compositions programmatically.

Fixes #7
Added support for multiple tracks in MidiGen.

Changes and Fixes

• I've added a new feature (provide details).
• I've fixed a bug (give a brief explanation of how it was resolved).
• I've made a breaking change (describe what was changed).
• I've made an enhancement to an existing feature (describe what was enhanced).

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Include any relevant details for test configurations and how to reproduce the tests.

Checklist:

• My code follows the code style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in areas that may be hard for others to understand.
• I have updated the documentation to reflect my changes.
• My changes do not generate new warnings.
• I have added tests that prove my changes are effective.
• New and existing unit tests pass locally with my changes.