Reproduce simple example

[ferrine]

https://github.com/pymc-devs/pymc3/blob/master/pymc3/examples/simpletest.py

I think that can be a milestone for any backend.
It requires API concept as well as stochastic parameters properly working

[sharanry]

Hey, can I take this up?

I can start by trying to run the the simpletest.py on code with pytorch, tensorflow, CNTK or/and mxnet as the computational backend?

[junpenglao]

Go for it ;-)
Maybe try with using tensorflow.distribution first.