Removed usage of sys.stderr in mock exception which caused the stream tobe closed. This in turn failed the next test.  Simplified test_search toavoid the zip and the loop.

Arguments realtime_start and realtime_end in get_series() now cause apandas.DataFrame to be returned with pandas.MultiIndex for realtimedata.  Added simple test for the new feature and documentation.Added __init__.py in fredapi.tests so it's correctly interpreted asa package. Now we could revert to python setup.py test in .travis.yml.Fixed test_invalid_kwarg_in_get_series() as we sometimes get aTypeError and sometimes a ValueError. Seems that pandas passes throughwhatever exception it gets, might be a good reason for this so wefollow the same policy.Simplified comparison of dataframe output in tests.

9999-12-31 cannot be converted to pandas.Timestamp because it's too big.Reason it's prefereable to use pandas.Timestamp than datetime.datetimeis that the former can be used as an index whereas the second cannot.