set up performance tests

[modeswitch]

Not sure if Mocha can handle this. I'd like to get performance tests running so we can start making performance improvements.

One way to approach this is to measure performance on each API call, then compare the results to native node.js. We should also track changes over time and catch major performance regressions.

This issue should cover getting a performance framework up and running with a few basic tests (not the entire API). Will open additional issues once this is done.

[modeswitch]

Marking this as critical. We're starting to demo things now and performance is becoming important.

[modeswitch]

https://github.com/js-platform/filer/wiki/Performance