Move change log into separate file?

Hi

I propose that we move the change log into a separate file. Perhaps a
simple txt or md. I don't think it's that common to have it in the spec.
The current setup makes it harder to search the spec for old and
deprecated API. You always get a few hits in the change log section
where an old method is mentioned. And it wouldn't hurt to make  the
document a few lines shorter. :)

/Adam