request: please organize the Changes page in sections

[Federico Bruni]

http://lilypond.org/doc/v2.17/Documentation/changes/index.html

While I was translating this page last sunday, I thought that it's not an
"easy read", even though it's addressed to users.

The current policy is adding the changes on top of the page during the
development cycle. So it's a kind of (reversed) chronological log of
changes.
I think that (lazy) users would benefit of a little more structured page.
I'm thinking about something very easy like just three sections:

1. syntax changes (this should be on top).
2. improvements/new behaviour
3. new features

What do you think about it?

We've already seen a lot of wrong bug reports about the new dot syntax,
questions about the bar commands not working, etc.

Also, I suggest adding a warning in the download page:
"If you are upgrading to a new stable version, you may need running
convert-ly on some of your files. The list of changes is available at....".