@starsirius => Add syntax highlighting and ruby evaluation to markdown rendering.

Syntax highlighting using Github flavored markdown and CodeRay.

![screen shot 2014-08-29 at 10 58 11 am](https://cloud.githubusercontent.com/assets/542335/4091889/f133355e-2f8c-11e4-9b2a-a2a920bca669.png)

![screen shot 2014-08-29 at 10 59 22 am](https://cloud.githubusercontent.com/assets/542335/4091909/18e2042c-2f8d-11e4-971c-66bdff0222c0.png)

Rendering tables inside documentation.

![screen shot 2014-08-29 at 10 58 43 am](https://cloud.githubusercontent.com/assets/542335/4091900/0217f526-2f8d-11e4-86d9-bd0fc3c894e9.png)

Allowing to render ruby evals inside markdown, for example `"#{Rails.app....}"`. This would obviously be unsafe if we didn't control and commit our own markdown files and rendered user content.

Removed all of the `succeed do ...` blocks, you can write plain html inside HAML that just works.
If this will be used in multiple pages, we could consider moving it to the `bootstrap_and_overrides` and override the [default style](https://github.com/twbs/bootstrap/blob/77b0dc69ebefb8c3ddb1b25a0bd51ef53c0d0e9b/less/forms.less#L215). Or we could scope it under this page (something like `start_show` if I remembered correctly) to avoid affecting forms in other pages.