Run all tests in parallel

[bahmutov]

To speed things up and to create a report for each dependency

foo@1.0.0: working
bar@0.2.1: breaking
baz@2.0.5: working

Pretty major enhancement

[ralphtheninja]

I was about to write an issue on this 😀 It would be a very nice enhancement. My use case is testing dependents for abstract-leveldown and it would be really useful to know the status of multiple dependents and not just abort on the first fail.