Toolkit methods getHumdrum and getHumdrumFile is not correctly named

[ahankinson]

The get* methods tend to return a value from the internal state of the toolkit, while the render* methods will render the toolkit data to a file. So getHumdrumFile(filename: str) -> bool should probably be renamed to renderToHumdrumFile(filename: str) -> bool to match.

Additionally, getHumdrum() -> str should probably be renamed renderToHumdrum() -> str