Merge pull request #42 from adriaanm/master

Merge 2.10.x into master.
reminder to update download/index.md
SI-1796 was reopened, partly subsumed by SI-6169
Added brief summary notes for (some of the) changes to collections.

This PR does not regenerate the HTML file.  A follow-on PR will have to do that.
Merge pull request #45 from Ichoran/ichoran/notes0

Added brief summary notes for (some of the) changes to collections.
SI-6566: Announce fix in release notes

Because of SI-6566, right-hand sides of type aliases are now considered invariant for variance checking. Mention this in the release notes, per discussion with @retronym [on JIRA](https://issues.scala-lang.org/browse/SI-6566?#comment-68243).
Merge pull request #46 from Blaisorblade/patch-1

SI-6566: Announce fix in release notes
WIP: 2.11.0-RC1 relates notes: breaking changes and deprecations

Will make a more comprehensive pass next week.