Parallel test runs

[ethanfrey]

Closes #89

This works faster but has 2 issues:

• Since test cases run in separate processes, the mutex only prevents conflicts within one file. We need to see how to prevent conflicts between files
• Sinon doesn't work to well in these parallel situations. (remove .serial from the binary tests to see this)

[willclarktech]

Sinon doesn't work to well in these parallel situations.

Without looking into this my guess is we can solve whatever the problem is with sandboxes: https://sinonjs.org/releases/v9.2.4/sandbox/

[webmaster128]

Looking at #254, can we close this?

[ethanfrey]

Let's close the PR for sure.

Maybe revisit the issue with the new framework (which must run everything sequentially at first until we refactor the startup code)