Added Exception inheritance checking

Includes new `ExceptionInheritanceOptions` enum to match the existing
  `ExceptionMessageCompareOptions`
Added `AssertExceptionNotInherited<T>` to `ExceptionAssert` and use
  from `AssertExceptionType<T>`
Updated unit tests in ThrowsTests.cs to include tests for what happens
  both with and without the new option; existing calls should work as
  they were so that nothing that depends on this library breaks.