Use github-markdown instead of RedCarpet

Because it is named 'gfm' style :-)
Stash plugin calls before applying markdown conversion
Merge pull request #2 from yhara/github_markdown

Use github-markdown
bump version to 0.1.0
to_html should not modify the given string (fix #3)
fix: test failed with Ruby 1.9 (refs #3)

`lines` returns Enumerator on 1.9, so we need `to_a`.
bump version to 0.1.1