Supports blockquotes prefixed by spaces

Currently markdown-js doesn't support blockquote characters prefixed by spaces. So `> hello' works but `  > hello` does not. This functionality should work if we're going by the [web dingus](http://daringfireball.net/projects/markdown/dingus) for markdown.

This patch adds a little scrubber to the blockquote functionality to support spaces in front. It also includes a test to make sure that if there enough spaces a code block will come into effect.