rename CHANGES to CHANGELOG & indicate breaking changes

[benjaminapetersen]

• CHANGELOG is just a suggestion, seems to be the best suggestion (I've seen) for a conventional filename (per something like this: http://keepachangelog.com/)
• The current changelog mentions no breaking changes, even for major version changes. True? If so, nothing to do here!

Thx!

[ljharb]

The breaking changes aren't explicitly called out, but https://github.com/es-shims/es5-shim/blob/master/CHANGES#L249 is a breaking change, for example, as was https://github.com/es-shims/es5-shim/blob/master/CHANGES#L290 and https://github.com/es-shims/es5-shim/blob/master/CHANGES#L309

[benjaminapetersen]

Curious if it would be possible/worth the effort to note each item in the changelog as bug fix, feature, breaking (or some variation).

[ljharb]

Totally possible, it's just not a convention I've previously followed in this repo (i do in other repos). I'll start doing it, regardless.

[benjaminapetersen]

Awesome!