Quick and dirty benchmark.

Sample output:

OkHttp [gzip, chunked, HTTP_11]
bodyByteCount=1048576 headerCount=20 threadCount=10
Requests per second: 121.0
Requests per second: 304.6
Requests per second: 379.1
Requests per second: 386.9
Requests per second: 369.2
Requests per second: 390.8
Requests per second: 368.8
Requests per second: 325.2
Requests per second: 409.4
Requests per second: 389.1
Merge pull request #499 from square/benchmarks

Quick and dirty benchmark.