Issue 8: Stubs cannot raise exceptions fix

Summary:
Corrected issue in stubs not being able to raise exceptions as per issue...#8 (https://github.com/nsigustavo/ludibrio/issues/8) and added unit test to verify functionality

Solution Summary:
-Added logic in stub.py to raise response if it was an exception. Previously it always returned.
-Added unit test to verify this functionality.

Here are the doctest results with no failures:

son@ubuntu:~/projects/ludibrio/ludibrio$ doctest
/home/jason/projects/ludibrio/ludibrio/specification/unit/mock.dt
TestResults(failed=0, attempted=29)

/home/jason/projects/ludibrio/ludibrio/specification/unit/mock_msg_error.dt
TestResults(failed=0, attempted=10)

/home/jason/projects/ludibrio/ludibrio/specification/unit/stub_proxy.dt
TestResults(failed=0, attempted=5)

/home/jason/projects/ludibrio/ludibrio/specification/unit/bug_getattr.dt
TestResults(failed=0, attempted=6)

/home/jason/projects/ludibrio/ludibrio/specification/unit/spy.dt
TestResults(failed=0, attempted=18)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/kind_of.dt
TestResults(failed=0, attempted=7)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/equal_to_ignoring_case.dt
TestResults(failed=0, attempted=9)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/ended_with.dt
TestResults(failed=0, attempted=4)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/less_than.dt
TestResults(failed=0, attempted=7)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/like.dt
TestResults(failed=0, attempted=4)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/custom.dt
TestResults(failed=0, attempted=5)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/specialarguments.dt
TestResults(failed=0, attempted=14)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/in_any_order.dt
TestResults(failed=0, attempted=8)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/started_with.dt
TestResults(failed=0, attempted=4)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/greater_than_or_equal_to.dt
TestResults(failed=0, attempted=8)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/into.dt
TestResults(failed=0, attempted=5)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/less_than_or_equal_to.dt
TestResults(failed=0, attempted=8)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/equal_to.dt
TestResults(failed=0, attempted=6)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/contains.dt
TestResults(failed=0, attempted=4)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/instance_of.dt
TestResults(failed=0, attempted=7)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/greater_than.dt
TestResults(failed=0, attempted=7)

/home/jason/projects/ludibrio/ludibrio/specification/unit/specialarguments/any_of.dt
TestResults(failed=0, attempted=5)

/home/jason/projects/ludibrio/ludibrio/specification/unit/stub.dt
TestResults(failed=0, attempted=28)

/home/jason/projects/ludibrio/ludibrio/specification/unit/dependencyinjection.dt
TestResults(failed=0, attempted=8)

/home/jason/projects/ludibrio/ludibrio/specification/unit/mock_unordered.dt
TestResults(failed=0, attempted=6)

/home/jason/projects/ludibrio/ludibrio/specification/unit/mock_and_stub_dependencyinjection.dt
TestResults(failed=0, attempted=8)

/home/jason/projects/ludibrio/ludibrio/specification/unit/stub_msg_error.dt
TestResults(failed=0, attempted=6)

/home/jason/projects/ludibrio/ludibrio/specification/unit/dummy.dt
TestResults(failed=0, attempted=36)

/home/jason/projects/ludibrio/ludibrio/specification/unit/dependencyinjection_importforadocontexto.dt
TestResults(failed=0, attempted=5)

/home/jason/projects/ludibrio/ludibrio/specification/functional/testdouble.dt
TestResults(failed=0, attempted=13)