Updated the Request#send_request method documentation.
Added a JsonSimple plugin to seahorse.

This plugin performs a naive translation of request params
the response bodies (to and from json).
Seahorse::Client::Base.define is now aliased as .extend

It also copies the API by default when extending.
Calling #body_contents now rewinds the #body attribute first.
Split logic in JsonProtocol plugin into two plugins.

Logic for populating the content-type and x-amz-target
headers have been moved into the JsonTarget plugin.  This allows us
to apply this logic only to JSON RPC clients (like DynamoDB, SWF, etc,
but not Glacier).
Regenerated JSON apis to list the multiple json plugins.
Added integration tests that perform simple JSON translations.

These omit:
* Param conversion
* Param validation
* Response structure generation

This should provide for the fastest possible experience when using
a JSON api.
Removed a redundant spec.
Split the three protocol handlers each into two handlers:

Each protocol handler is now broken into parts:
* A request handler responsible for serializing params
* A response handler responsible for parsing responses

This allows us to share handlers across protocols, e.g.
query uses the xml response handler.
Request handlers can now populate the body themselves.
Removed a feature file that was left behind as a copy.