Port map benchmark to benchpress

[jeffbcross]

No description provided.

[ktrott]

RxJS Next meeting discussion:
(attendees: @Blesh, @jhusain, @trxcllnt)

• flatMap is in benchpress right now.
• need to identify what are several really good macro performance tests

We'll create a new issue on the macro perf tests

[benlesh]

I think at this point we probably don't need macro perf benchmarks for simple operators. Micro perf is probably fine for these. Macro perf, on the other hand is a necessity for any of the operators that are internally creating new observables, or subscribing multiple times to inner observables.

Closing for now in favor of #126