Basic note generation was tested and the headers seem to be correctly formatted, is now played by most midi players.
Removed trivial getters/setters and extended the messages a bit. They are no longer hardcoded and any message can now be created. Furthermore, I have decided to keep this library low-level. Another library will be created later, which will use all the basic functionality in this one, to better reflect the structure and hierarchy of music. This library should be able to arbitrarily write to any sound type however, so therefore I have decided to make this library a part of that one.