Rename README.rdoc to README.md

It seems like rdoc is converting the teardrop ' into an angled apostrophe ’ ... which is no fun for coding (and copy/pasting). rdoc also seems to not support fenced code blocks with the three backticks ```
FIX: add var to stop global leak of Sanitizer
Merge pull request #15 from jesseskinner/fix-global-leak

Add var to Sanitizer declaration to stop global variable leak
Merge pull request #12 from gh-naylor/patch-1

Rename README.rdoc to README.md
Bump version to 0.1.2
Clean up Readme to use Markdown