added COBYLA (no REST interface yet)

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: denizokt_370_constraints
Ticket(s)/Issue(s): Closes #370 

********* TESTING DONE *************
make test
make style-test
this is severely under-documented.... why do you need start_index?

Also the scipy docs make it sound like x >= 0 is *required*: Constraint functions; must all be >=0 (a single function if only 1 constraint). Each function takes the parameters x as its first argument.

also have you checked that these constraints give you what you want? how does "lambda" capture local variables in python?