Improve Throw assertions

[vbreuss]

From #871:
Refactor the delegate assertions as follows:

• Add the following methods to the IDelegateSource<TActual> interface:
  • .ThrowsNothing() (no exception is thrown)
  • .ThrowsException() (any exception is thrown)
  • .Throws<TException>() (an exception of type TException or any subtype is thrown)
  • .ThrowsExactly<TException>() (an exception of type TException is thrown)
• For all thrown exceptions we have
  • .WithMessage(string) (checks that the message is equal)
  • .WithMessageMatching(string) (checks that the message matches the (wildcard) pattern)
  • .WithInnerException() which allows checks on the inner exception