Add shuffle_batch fit arg

[jfkirk]

Came up in https://github.com/jfkirk/tensorrec/pull/31

It would be nice to have an arg to re-order the batches every epoch while fitting.

• [ ] Add shuffle_batches arg to fit() and fit_partial() that shuffles the batch order every epoch if True
• [ ] Add tests for the arg

[kevglynn]

@jfkirk just getting into this. Want to make sure, just aiming for reordering the order of the actual batches?

Assuming 3 batches:

• epoch 1 evaluates on batch[0], batch[1], batch[2]
• epoch 2 evaluates on batch[2], batch[0], batch[1]
• and so on

is that correct? Initially, I had been thinking we were going to shuffle all of the items amongst the batches, but reading above it sounds like that is not the case.