Add changes for 0.9.0 for History.rdoc

Generated from `git log --oneline v0.8.0..HEAD | grep 'Merge pull request'` then manually edited. cc @mtodd @schaary. Add a date when we decide to release.
1.9+ has actually been required since 0.5.0. Clarified in 96170f3c392c499c3685fc678051a2e41ad3f85d