Add attribution for #306 to release notes
Clean up capturing tests
Raise unmet dependency error instead of manually recompiling
Add release note
Merge pull request #337 from nanoc/bug/double-compilation-when-capturing

Double compilation when capturing
Add test for current enable_utf8 behavior
Recognise en_US.utf8 as UTF-8 (fixes nanoc/nanoc#335)
Merge pull request #338 from nanoc/bug/case-insensitive-utf-8-check

Allow lowercase environment variables in UTF-8 check
Add lowercase UTF fix to release notes
Merge branch 'release-3.6.x' into release-3.x