ivy: fix bug in rational **

problem was overwriting the num and den of the LHS.
x=1/2
x**2
x
printed 1/4 instead of 1/2

the test results were wrong, too. so much for golden tests.

Change-Id: Iaa7fdca90a9aad37ad92d8f8155d33115f43240d
ivy/talks: add support files for running the demos

Change-Id: Ife060cfa993743cd650b4c46092ac2b6f4f201b9