Support testing rspec 2.14/2.99/3.0
Move role that backtrace cleaner to formatter class

Don't have to clean backtreace when runtime error...
Unuse PendingDeclaredInExample.

No need create PendingDeclaredInExample...
Separation code that depends on RSpec 2
Support custom formatter on RSpec3
Catch the error rspec-expectations matcher throws

Since Rspec3, ExpectationNotMetError is no longer subclass of StandardError.
Don't use reserve key of example metadata when initialize

     RuntimeError:
       **************************************************
       :file_path is not allowed

       RSpec reserves some hash keys for its own internal use,
       including :file_path, which is used on:

         /path/to/turnip_formatter/spec/support/example_helper.rb:22:in `base_example'.

       Here are all of RSpec's reserved hash keys:

         description
         example_group
         parent_example_group
         execution_result
         file_path
         full_description
         line_number
         location
         block
       **************************************************
Switch pending method RSpec 2.x/3.x
Smart smart smart
Merge pull request #46 from gongo/support_rspec3

Support RSpec 3 [True]