Minor refactoring to allow for restish-like child traversal for
responder location.
Add a property to directly access all parameters.
Handle the case where POSTed keys appears more than once.
Add missing tests - full suite now passes with py27,py34.
Response to code review:

 * Document the params property as a dictionary mapping query string keys to
   values.  Where the keys appear multiple times, the value is documented as a
   list of values.

* Moved the definition of the @property params to colocate with the other
  class properties.

* Added a NOTE(warsaw) as requested.
Merge branch 'refactor' of github.com:warsaw/falcon into refactor