doc: Add CHANGELOG
doc: Add CHANGELOG

A place to call out breaking changes, noteworthy enhancements/fixes, and
other "notice"-type advice.

I went back and populated this for the last few months, back through
most of 2016, but the repo itself dates back about 8 years at this
point, so I am not going to bother with the full history.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent