Add a TestRunner that uses fuzzer for random generation.

[Eh2406]

If I understand correctly a big part of what a Strategy does is convert randomness from a TestRunner into a specific type, so that a test can be run on it. And a large part of the work in running cargo-fuzz is making a fuzz_target that takes &[u8] and converts it into something worth testing. So if we had an alternative TestRunner that could use &[u8] as its source of randomness, then it would be easy write a fuzz_target that can use the excellent syntax of proptest to define its assertions. (and possibly get shrinking for free.) To put it differently this would allow code reuse between the growing library/ecosystem of proptest Strategys and the ecosystem of fuzz testing.

cc blt/bughunt-rust#2
cc https://blog.troutwine.us/2018/10/08/hunting-for-bugs-in-rust/

[AltSysrq]

I believe 0.9.1 has what's needed here.

let entropy: &[u8] = get_some_bytes();
let mut runner = TestRunner::new_with_rng(
    Config::default(),
    TestRng::from_seed(RngAlgorithm::PassThrough, entropy));

Please reopen if this addition isn't sufficient.