Read .mxl as .zip, and get the xml inside, also write .xml with same xml text

[AldaronLau]

.mxl is a compressed version of the .musicxml file. Despite the extension, it is actually a .zip file. We should have a musicxml crate in the root of the project. The first step in creating this crate is to have ZIP file reading and writing.

Read MXL and write MXL zip file.