setup benchmarking against RABL

Before we begin developing Nm, I want to have benchmarks in place
for a known templating system.  I am choosing RABL b/c I've used it
before and it does both JSON/BSON template outputs like Nm will.

This sets up running benchmarks using Whysoslow against a slideshow
template.  As Nm becomes ready, we can add it to the bench script
and see how it performs compared to RABL and make sure we aren't
introducing massive performance degredations.

@jcredding ready for review.