Update docs/plugins.rst

Change yuicompressor to yui_js and yui_css
Updated markdown reader to parse summary metadata as markup.
Updated unit tests to test markdown summary metadata.
Cleaned up markdown read.
Store slugs in posts by default on Pelican import
Merge pull request #577 from davidjb/import-improvements-slug

Provide slug storage option for posts during Pelican import
Merge pull request #635 from michaelreneer/markdown-summary-metadata

Updated markdown reader to parse summary metadata as markup.
Merge pull request #620 from rskvazh/patch-1

Update docs/plugins.rst
update the version of jinja needed, 2.6 is out
pep8/style matching
Merge pull request #655 from wraithan/master

tiny bit of code clean up
Improve Publishing to GitHub section of the doc
Fix the THANKS file.
remove duplicates
Fixed a typo

BeatifulSoup -> Beautiful Soup
Merge pull request #674 from peterdesmet/patch-2

Fixed a typo
Merge pull request #658 from elemoine/github

Improve Publishing to GitHub doc section