Refactored to remove UriSigner.
In order to do this I had to invert a switch statement that selected which RequestHandler to use based on your request method, so now the RequestCoordinator ctor signature has changed to take an IEnumerable<RequestHandler>.
This may cause a breaking change to the way you instantiate an instance of FLuentApi, but if your using a decent IoC framework you shouldnt have a problem.

Ive included a static RequestHandlerFactory that sets up the concrete Get and Post request handlers for now.

THis work is necesary not only for making replaceing the OAuth with the Crenna library, but also in order to support requestng the api with non GET and POST verbs in the future.
Merge pull request #109 from gregsochanik/crenna-oauth

Refactored to remove UriSigner.
Rename "ConstructBuilder" to "FindRequestHandler"
as "ConstructBuilder" is a weak name that no longer accurately describes what this does
Also more detail in the error message
renamed "EndpointResolverTests.cs" to "RequestCoordinatorTests.cs"
as that is now the name of the class under test
Get access token from environment variables or app.config

This allows the 3 legged access token tests to be run from CI builds
Merge pull request #110 from AnthonySteele/rename_internal_method

Rename "ConstructBuilder" to "FindRequestHandler"
Merge pull request #111 from AnthonySteele/rename_rc_tests

renamed "EndpointResolverTests.cs" to "RequestCoordinatorTests.cs"
Merge pull request #112 from mattgray/crenna-oauth

Get access token from environment variables or app.config
Basic tests on get and post request handlers
Merge pull request #113 from AnthonySteele/request_handler_tests

Basic tests on get and post request handlers
Rename UriPath to Endpoint, more accurately reflecting purpose
Rename IsSigned to RequiresSignature, more accurately reflecting purpose
Make RequestHandler.ConstructEndpoint protected
Construction of query string / post body from parameters happens at latest possible stage, to aid OAuth signing
Remove unused shouldEncode parameter from DictionaryExtensions
Use OAuth library for signing GET requests
Add Accept: application/xml header to every request
PostRequest request body is a string, not a dictionary
Post requests are signed using OAuth library
Remove unused ToQueryStringNoUrlEncode method