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.