Performance issues in the program

[DLPerf]

Hello,I found a performance issue in the definition of tensorflow_session ,
itdxer/neupy/blob/master/neupy/utils/tf_utils.py,
session = tf.Session(config=config) was repeatedly called and was not closed.
I think it will increase the efficiency and avoid out of memory if you close this session after using it.

Here are two files to support this issue,support1 and support2

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.

[itdxer]

Hi @DLPerf,
I've seen this problem and I believe at the time I didn't see a good way to solve it. When I switched neupy from theano to tensorflow I wanted to avoid using context for sessions, but overtime it proved to be a problem. I have some "hacky" fixes in the notebooks somewhere but never got around fixing the main problem. How do you suggest solving the problem?