Multi framework

Hi @asbjornu,

Got a better solution to the multi framework issue.

I added new Release and Debug configurations for frameworks 4.0 and 4.5, than I added a new file SharpRaven.build, to build for both frameworks.

At TeamCity, before rebuild, change the following properties for the MSBuild step:
 - Build file path: src/SharpRaven.build
 - MSBuild version: MS .NET 4.5 or MS Build Tools 2013
 - Targets: BuildAll

And for the Unit Tests step change the "Run tests from:" to the new net45 output path "src\tests\SharpRaven.UnitTests\bin\Release\net45\SharpRaven.UnitTests.dll".

[]'s
Bruno Oliveira