added helper function to transform entity into an update
added failing test
assignee field may be null
use opt-in attributes to indicate when a null property should be sent
added overloads for Delete to accept a payload
added tests and new method
corrected return type from Add
wireup delete API
corrected docs
updated observable clients
fix impacted test
implement a lookup of the fields/properties which should serialize null values
Update README.md
test for all issues being returned
Merge pull request #528 from octokit/shiftkey/another-integration-test

a teeny tiny test
Merge pull request #527 from octokit/shiftkey-patch-1

Added instruction for Xamarin Studio
Merge pull request #526 from octokit/unassign-issue-from-milestone

unassign milestone from issue
Merge pull request #524 from octokit/user-emails-delete

Add support for deleting emails for the authenticated user