Update README to support relative asset links

As of January 20th, GitHub supports relative links to assets within a
repository. See [this blog
post](https://github.com/blog/1395-relative-links-in-markup-files) for
more information.
Add Molokai theme

Colorscheme based off the
[molokai](https://github.com/tomasr/molokai) for vim.

Differences from the Monokai Soda theme:

- The third color (33, 34), which is traditionally yellow is a pastel
  yellow compared with orange (33) and yellow (43)
- The fourth color (34, 44), which is traditionally blue is a pastel
  blue compared with a lavender purple
- The fifth color (35, 45), which is traditionally magenta is a pastel
  purple compared with a (repeated) pink color
- The background color is slightly darker