requiring rdoc and removing redcarpet

* Without the rdoc declaration, the rake command failed.
* Redcarpet is not being used since March 12 2013's commits and
  can be removed
Adding link to the FuzzyLayout extension

(Read that as shameless self promotion)
Use bundler for gem management

* Added a Gemfile
* Modified the installation instructions in README.md to reflect
  these changes.