Upgrade to .NET4.5 and VS2013 RC+ support

Hi Sayed,
these are the changes I made to the solution to get support for VS2013, it was as simple as editing the source.extension.vsixmanifest file. The other files (sln, csproj) were updated by VS2013 during the upgrade process. I'm not sure about the `SupportedFrameworkRuntimeEdition-MaxVersion` though, if it should be `4.5` or `4.5.1`. All unit tests passed.

This is my first ever Pull Request, so please let me know if anything is not how it should be.

Hope this helps!
Cheers,
Roel