Experiment with including fuzz + mutation tests in the template

[leighmcculloch]

Experiment with including fuzz + mutation tests in the template.

There's a balance between making a template that's too overwhelming that turns folks away, so I'm not sure we want to do this. There's a couple options here:

• Try this out, and decide not to change the template.
• Try this out, and decide to include full boilerplate for fuzz and mutation tests.
• Try this out, and decide to just include a README comment that says "run cargo fuzz init to setup fuzz tests", and that says to "run cargo mutant to run mutation tests".