Added support for Caliper's ReBench output

- also fixed the support for harnesses reporting results for multiple benchmarks at the same time
- in general, the harness should be the 'benchmark' named in the config, not its subbenchmarks
- subbenchmarks are just criteria of the same 'benchmark' for simplicity at the moment…
- added tests, but not very complete/specific ones, except for the parser

Signed-off-by: Stefan Marr <git@stefan-marr.de>