Testing fenced code blocks

Will try to add my own support for this.

Will make it available, regardless of what markup language that I'm using, similar to my other custom formatting commands.

My custom fenced code block command code. / code.. is available when I'm typing in Textile or Markdown/Multimarkdown. The feature limits the window size that displays the code. So if it's a large blob of code, a small read-only text window with vertical and horizontal scrollbars displays the code.