CLI argument 'period' changed to 'observations'.

So now you get to specify the number of observations you want in the
course of the benchmark, as opposed to the period at which they occur.
This is more consistent witht the way I have been using it.
Added sorted match query to the benchmark.

Analysis is still mostly manual (what queries are there, how results get
grouped - adding new query to the benchmark should not require any
changes to the analysis code - this should be inferred from the
benchmark record itself).
analyze.py updated with the 'dump' option.

This allows benchmarks and their observations to be dumped as curl
commands, so that they can be saved and restored (of the es index goes
away or whatever).