Update 2014-12-08-plugins-release.md

Remove `closes x` references.

It's not relevant which PR was closed by a commit for the blog post imho.
Add platform prefixes to those readme lines missing them
Remove administrative tasks from notable changes
Remove minor documentation changes (except when they were fixing bugs)
Minor tweaks; capitalization, etc
2014-12-08-plugins-release: Markdown: newline after sections
2014-12-08-plugins-release: drop -, :
2014-12-08-plugins-release: drop tests
2014-12-08-plugins-release: drop plugin name
2014-12-08-plugins-release: fix Markdown
2014-12-08-plugins-release: fix grammar