#15 Unsaved changes detection too strict

[Robert Keller]

The detection for unsaved changes, in Notate.java, compares the before- and after- files as literal text strings. This is too strict. For example, if a leadsheet is written on a Mac, but read on a PC, then differences in ends-of-line will cause changes to be perceived, even though there aren't any.

A possibly better way would be to write a string representation immediately after the leadsheet is read in, then when closing, write a second representation and compare those to each other.