Ref. #2, #7 - Finish rewrite of test suite

- Corrected a bug in the Action#as_json method with used symbols where
  a string key should have been used instead
- Corrected the Action#controller and Action#action methods to look in
  either the string or symbolized versions of their associated params
  attributes, to make sure they were included in the json output
- Finished writing the tests for all current metric classes
- Fixed a typo in the test/lib/how_slow_reporter_test.rb file since it
  was still describing the module and not the Reporter class itself.
  This was an oversight in the changing from module-based reporting to
  class-based reporting.