L-BFGS-B Implementation

Very rough at the moment. Uploaded for potential comments/suggestions.

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: denizokt_228_implement_LBFGSB
Ticket(s)/Issue(s): Closes #228 

********* TESTING DONE *************
make test
there should be a newline after this. always 1 line btwn last line of text and the ```"""```. here & elsewhere.

idk why style check isnt catching these