Many small changes

1. Use nanos until the end
2. Reuse executor service, resize when needed
3. Cycle through input file in Step command
4. Use ByteStreams.copy in Fist
5. Embed $JAVA_OPTS placeholder into the executable jar
6. Fix request rate calculations
7. Add some more basic stats to Step's report

Also, split construction and invocation of Fight from Step
Makes sense since we're spawning all the threads of the threadpool from
within the constructor.