[feat] add reporting

[aaronc]

Not sure how useful it is to have additional reporting. It seems like the official standard is Cucumber Messages and that would allow using the Cucumber Reports service: https://cucumber.io/docs/cucumber/reporting/.

I did a bit of a PoC on this in this branch several months ago: https://github.com/regen-network/gocuke/tree/aaronc/reporting.

If anyone finds this useful, that work could be picked up.

I think I had this branch more or less working but couldn't get things to display correctly with cucumber reports. One oddity with the go test runner is each test file or package is more or less run in isolation. So the hack I had to do to make this work is to save the log file for every test run, but then pick up where it left off: https://github.com/regen-network/gocuke/compare/aaronc/reporting#diff-49c34b1e1ce730ef828f61b8e3ed089ea2397972b1930d4fdb43854222641eb2R81-R85. The alternative is to not use the go test runner but my opinion is that this is a worse tradeoff.