Sort added/removed/modified encoded glyphs by Unicode

[jenskutilek]

I have to compare fonts with lots of changes in the character sets, and the glyphs are shown in random order. It would be much easier to get an overview of what has changed if the glyphs were sorted by Unicode codepoint.

[simoncozens]

The idea is that the glyphs are ordered by amount of change. But we should make sorting by Unicode an option as well.