Stubbed out the API for pull requests.

Still missing pull request files, commit lists and merge checks.
Stubbed out the reactive Pull Request functionality
Tested out all of the existing Pull Request code

Still missing integration tests for Pull Requests, though.  I need to do
a bit more research before I can start to tackle that one.
Fixed some goofed up test names
Documented missing properties; Whitespace and typo tomfoolery patched
Referenced pull request functionality for Mono projects

Manually referenced as this requires Xamarin studio to do automatically.
Implemented pull request merge functionality
Merge comments default to an empty string as they are optional.
Patched up some issues from the upstream merge.

Removed default parameter from pull request merge message according to
CA1026.
Added tests for the Merge method
Implemented Merged? functionality / tests

Bugfix for building the merge api url, as well.
Unit test fixes
Pull request commit list now implemented / tested

Renamed and enhanced existing Merged tests.
PullRequest model now contains all of necessary fields

- Initial integration test for pull requests (can't seem to do much
without the tree api)
- Added Observable unit tests for the rest of the pull request client
Merged now returns bool based on the request http response
NewPullRequest required parameters altered

NewPullRequest constructor only takes required params.  Each required
parameter is now a readonly property.
Fixed auto properties and moved integration tests around
Killed with the hottest fire.
fixing all the merge conflicts
the unit tests now pass