Some bug fixes, a few added features

[alejandroschuler]

• shareglrm can now take an array of Y-regularizers, just like glrm
• added periodic and imbalanced hinge loss functions
• bug fixes

[madeleineudell]

This looks great. Just a few changes and I'll pull:

• can you add the mathematical definition of the new functions (periodic and imbalanced_hinge to the comments preceding them, and add them to the README?
• would you mind changing the name of imbalanced_hinge to unbalanced_hinge or weighted_hinge?

[alejandroschuler]

No problem- weighted_hinge is much better. I'll do that in a bit.

[alejandroschuler]

Alright, the changes have been made. Check it out and let me know if everything is satisfactory.

[madeleineudell]

closes #4