Fixed bug introduced by pep8-cleaning of mlp.py

Apologies; in the previous pull request, I had introduced a bug by splitting long lines of the form:

    updates[W] = updated_W * (desired_norms / (1e-7 + row_norms)).dimshuffle(0, 'x')

to:

    unshuffled = updated_W * (desired_norms / (1e-7 + row_norms))
    updates[W] = unshuffled.dimshuffle(0, 'x')

This PR reverts these lines to their previous, pep8-violating but unbuggy forms. It also includes pep8 fixes to costs/cost.py, and adds some items to .gitignore.