After writing `x = Conv2D(...)` one can access the used variables
by `x.variables.W` and `x.variables.b` if they exists.

This is much better than writing:
`x.name.replace('/output:0', "/W:0").replace('tower0/', '')`

whould would also break the InferenceRunner.

* add max_p to psnr

* Update symbolic_functions.py

* fix liniting and remove name_scope

* solution from issue 207

* remove copy

* remove old docs