Merge pull request #14 from luchoooo/master

Fixes on TransferEncoding and Trimming bug
Preparation for 4.0 RTM.

- Added new test cases for handling malformed event streams.
- Added new test case for SendGrid's new event test payload.
- Added Portable.Mail.MailAddress.ToString() to fix a failing test.
- Added new SmtpId property to the EventData object.
- Fixed a bug where headers were not being added to a message properly.
Update NuGet packages to support WP 8.1
More cleanup.
- Added WP8.1/Universal Apps support.
- Update WP8 sample to WP8.1
- Update NuGet dependencies to very latest.
- Fix async to prevent deadlocks.
- Incremented NuSpec file to 4.0 final and fixed package references.
- Fixes to allow for events to be re-serialized (for example, when being used with Windows Azure Queue Storage).