Sclark 384 blog ab example

********* PEOPLE *************
Primary reviewer: @suntzu86 

Reviewers:

********* DESCRIPTION **************
Branch Name: sclark_384_blog_ab_example
Ticket(s)/Issue(s): Closes #384 

********* TESTING DONE *************
manually run
make test
make style-test
this seems unrealistic?
you generally can't just sample the objective function whenever you feel like it.

unless the implication is that users should have a 'db' of objective measurements that they can access from wherever (vs storing the relevant data in the arms)