Make the build work on Window 7 machines.

Check for windows version and don't build the WinRT project unless we're on Windows 8 or better.
Merge pull request #26 from joshrobb/fix_win7_build

Make the build work on Window 7 machines.
Update README.md
Auto unwrap HttpUnhandledException

The module will typically be seeing HttpUnhandledExceptions which
contain the useful exception details in .GetBaseException().
Automatically unwrap this before sending it to Raygun.
Merge pull request #27 from MindscapeHQ/unwrap-httpunhandledexception

Auto unwrap HttpUnhandledException
Update README.md

Updated README
Update example code to unwrap exceptions so sane data gets recorded.
Add SendInBackground method to deliver exception report from a Threadpool thread.

Extract common code for BuildMessage.
Use SendInBackground to deliver asp.net exceptions in a background thead.

Remove duplication - only validate the API key in one place.
Merge pull request #28 from joshrobb/readme-manual-unwrap

Update example code to unwrap exceptions so sane data gets recorded.
Merge pull request #29 from joshrobb/background-thread-send

Background thread send
Use UTF8 encoding
Update README.md