Don't group slow tests

[egonelbre]

This allows -slow 5 to limit output to only 5 slowest tests, or -slow -1 to all slowest tests.

Fixes #34

[mfridman]

Thank you for submitting a PR. 🎉

I think you're right, more often users would want n number of slowest tests regardless of pkg, so let's give this a try.

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I think in the future it'd be nice to consolidate the logic, e.g.,

• sort pkgs by name
• iterate over pkg and add skipped/passed (depending on options)
• sort passed by time
• add skipped and passed to a var all []*test

then check if slow is available and do some logic relating to that, otherwise iterate over all and add "line break" whenever pkg changes.

[egonelbre]

For consolidating logic, I was trying to avoid too large refactoring since you have the path towards v1 issue.

[mfridman]

Awesome. Thanks for contribution.