add GitHub Flavored Markdown to README

* This makes the example code easier to read,
  especially when perusing the docs on github
Merge pull request #16 from phlipper/patch-1

add GitHub Flavored Markdown to README
Bump gem version in Gemfile.lock
Support short-hand rendering of partials

Before: required syntax for rendering was:
`render partial: 'partial_name', collection: @collection, cache: true`

After: `render @collection, cache: true` works as well.

`cache: false` also disables caching as well now.
Use respond_to?(:call) instead of is_a?(Proc)
Remove trailing whitespace
Update README with new supported syntax