dynamically install rest-client

Proposed hacky fix for #34.

@evalencia @salgo @jeffbyrnes @edwardvfluke  could you try this fix?
Seconded.  The "right" way to do this would be to make the connection an object itself (by defining a new class) and then put the `require` in the initialize method for that class.  It would also allow you to remove a lot of redundant code from the other methods.