Adding rspec support for several command line options

I've added support for several rspec options, including:
  - --require
  - --format
  - --out
  - --example
  - --tag
I've simply ported over the descriptions from the original rspec/core/option_parser.rb.

The workaround for supporting --out is to write the output to several files and then merge the results together after test execution.

Let me know if you see anything out of the ordinary. If not, please pull into the master repo and then apply to the gem. I'm new to Ruby and gems, so I'm not sure how the gems are republished after updating code.