Dn M MusicXML Versions Save

@DJBen and @bwetherfield made great strides in improving the decoding process (e.g., #201, #203, #204, #206) and standardizing the API (e.g., #207, #208).

Under the hood, we added all of the MusicXML sample files to the test suite, and made the testing infrastructure more flexible.

• Score is now the first-class citizen of the MusicXML package
• Header elements have been fixed
• Generalized testing infrastructure has been added (thanks @DJBen!)

Pre-release version 0.2.0 now successfully parses the LilyPond test suite in its entirety, with the exception of two tests:

• Compressed-MusicXML, which is not yet critical to support yet
• PartNoId, which is invalid as per the MusicXML specification.

Thanks to @DJBen and @bwetherfield for making this possible 🎉 !

Provide a model and API for deserializing only the "Hello World" example provided by MakeMusic.