add to docs for simplemusic and minor fixes in simplemusic.py

[palmerev]

In simplemusic.rotate the parameter is now "notes" instead of "item", which better describes the input as a collection instead of a single item.

Please let me know if there is anything else you'd like for the documentation. I plan to add more in the future when I have time.

[kroger]

Thank you for the patch! It looks good. I try to use PEP 0257 and it says:

The docstring is a phrase ending in a period. It prescribes the function or method's effect as a command ("Do this", "Return that"), not as a description; e.g. don't write "Returns the pathname ...".

Therefore, could you, please, change back "returns" to "return" and so on? After the change I'll apply the patch.

[palmerev]

OK, I made the changes.

[kroger]

Thanks!