Use BlueCloth to render Markdown

Rather than starting a subshell and calling the markdown executable each
time we want to render a Markdown file, use the BlueCloth gem. It's
faster and more robust, plus easier to maintain cross platform.

This patch fixes the broken Markdown doc rendering on SUSE.
Merge pull request #481 from jamestyj/bluecloth

https://github.com/crowbar/barclamp-crowbar/pull/481

Merged by devtool for cloudedge