Introduce fuzzer input compilation from known program bytes

[techraed]

Problem to Solve

Currently runtime-fuzzer inputs and corpuses are generated from external crate (which is libFuzzer) and are used to instantiate an Arbitrary implementor. But currently there's no way to do the job backwards: convert interesting program or set of gear calls into bytes that runtime-fuzzer will use to instantiate from them same types with same data.

The main aim here is to have a way to define own corpuses, not generated from libFuzzer.