Adds the AsyncRelatedTests fixture with a single test illustrating https://github.com/tpierrain/NFluent/issues/112 (ignored for the moment)

Migrates NFluent from .NET 4.0 to .NET 4.5 to prepare the compliance with Async/Await concept.
Introduces comments to exclude MS tests integration stuff from NCrunch coverage (see within ExceptionHelper type) which restores test coverage to 100%.
Temporary fixes a NCrunch issue with conditional compilation symbols (here: dotNet45) : http://forum.ncrunch.net/yaf_postst935_Issue-when-using-conditional-compilation-symbols-in-linked-file.aspx
Workarounds a NCrunch issue when using conditional compilation symbols (http://forum.ncrunch.net/yaf_postst935_Issue-when-using-conditional-compilation-symbols-in-linked-file.aspx) by forcing the DOTNET_45 symbol for all possible configurations of NFluent.40 and NFluent.40.Tests projects.

The issue was that none of the code or test depending on this conditional compilation symbol was taken into account by NCrunch.

Note: that one was painful to troubleshoot and to fix.
Renames NFluent.40.* folders to NFluent.45.*
Updates build script to be able to target .NET 4.5 instead of .NET 4.0.
First and naive implementation of Check.ThatAsyncCode() + tests (still failing so far).
Fixes some comments.
Replaces the InvalidOperationException by a SecurityException. InvalidOperationException was hidding the failure of one test.
Here comes the green for the AsyncRelatedTests. Next step: refactor ;-)
Fixes all AsyncRelatedTests, reorders them for a better readability, adds some comments with questions for reviewers

Fixes all stylecheck issues.
Improves unit test comment.
Improves release note.
Follows @mareek advices to simplify type inference between async methods and async functions.
Gets rid of AwaitableFunction and AwaitableMethod delegate types.

Simplifies Generic signatures for async related checks.
Adds a CheckThatAsyncCodeWorksAlsoWithAsyncLambda() test to show @Cyrdup an example.
Restores NFluent.40 (instead of NFluent.45). Only NFluent.40.Tests will continue to target .NET 4.5 (for async/await usage).
Renames all NFluent.45.* directories to NFluent.40.*
Sets the new version number for NFluent: 1.3.0 (following the semantic versioning)
Fixes the NFluent.nuspec file in order to target .NET 4.0 instead of 4.5.
Fixes a StyleCop curly bracket issue.