* custom mutator rust support
* clarify how to view documentation for rust mutators
* remove `FuzzResult` hack and clarify lifetimes of CustomMutator::fuzz
* rename TErr associated tyep to Error to be more idiomatic
* fix warnings
* add example for fallible custom mutator
* make Fallible Custom Mutator the default and implement it's handle_err method by default
* rename CustomMutator::handle_err to handle_error
* add example mutator using lain