Upgrade 0.9.0 - Githubissues

[x] Create new milestone for release. Move issues and PRs from Next Minor/Major Release into it.
[x] Bump version numbers. ack -Q 0.8.7 and replace with 0.9.0 where appropriate (this needs to be automated)
[x] Draft new GitHub release tag 0.9.0 on master.
[x] Add changelog to release notes.
[x] Add contributor props to release notes.
[x] Copy changelog and contributor props HTML to readme.
[x] Build ZIP via grunt build; cd build; zip -r ~/Downloads/customize-posts.zip *; cd -
[x] Add link to readme in tag release notes: https://github.com/xwp/wp-customize-posts/blob/0.9.0/readme.md#changelog
[x] Test build.
[x] Merge release PR.
[x] Deploy to WordPress.org via grunt deploy. Remember to look at SVN diff.
[x] Publish GitHub release.
[x] Close GitHub milestone.
[x] Merge master into develop.

xwp / wp-customize-posts