Encode title data

[adrianholovaty]

The old spec had a simple <title> element to encode the piece's title, but I deliberately didn't migrate this to the new spec, as it seemed half-baked.

We should at the very least handle the various cases MusicXML handles — including the elements within <work> and the separate <movement-title>.

Issue #56 treats this more broadly, and I'm leaving that open for the time being.

I think a good argument could be made for the simplicity of using a single <title>, but it should be designed in a way that can handle the other types of titles/subtitles elegantly.