add rouge and redcarpet to gemspec
create preview features
create the markdown features
added rouge css
moved blog_markdown into lib

moved blog_markdown module into lib. added tests that are independent
from blog_post model.
fixed some specs

moved a generator line to a newline. refactored a blog post controller spec
removed unnecessary require
Merge pull request #38 from mixandgo/feature/redcarpet_markdown_r0

Feature/redcarpet markdown r0