Added custom markup load based on the existing tags.

- The current implementation of org-ruby doesn't give
  the option to enable custom markup for HTML or Markdown.
  This commit enables that functionality, it's a matter
  of passing the correct markup file in the options.
Added documentation about custom markup to README.rdoc
Fixed bad equivalence.
Updated to rspec-3.0.0 deprecated failing specs.
Update everything to rspec 3.0
Stick to ASCII on the Readme
Merge 'custom-markup' branch from gnusosa (fixes #16)