Loosen ruby2ruby dependency

Since ruby2ruby is sementically versioned, we can safely allow any 2.x
version equal to or above 2.0.8.
Use byebug on MRI 2.0 and up
Update to RSpec 3

Conversion involved the following steps:
- Use transitional RSpec version 2.99
- Convert specs to RSpec 2.99.1 syntax with Transpec
- Simplify converted specs that used to use 'its'
- Update dependency to RSpec 3.0
- Remove rcov options from rake tasks
- Remove deprecated RSpec config option from spec_helper
- Use current matcher protocol for smell matchers
- Update matchers used in step definitions
- Improve some expectations by using operator matchers
Merge pull request #264 from troessner/issue-263-loosen-ruby2ruby-dependency

Loosen ruby2ruby dependency
Bump version to 1.3.8.
Merge pull request #267 from troessner/update-to-rspec-3

Update to RSpec 3
Merge pull request #265 from troessner/use-byebug-on-ruby-2

Use byebug on MRI 2.0 and up