Deprecate fuzz_catch_panic

[leighmcculloch]

What

Deprecate fuzz_catch_panic, encouraging developers to use the try_ invoke functions instead.

Why

The fuzz_catch_panic function catches panics that occur when the contract fails and generates a panic. It is necessary to often catch panics when testing contracts because contract errors are populated up to the test as a panic when called from their regular client invoking function.

However, contract clients, and the env, also have try_ variants of each function for calling a contract. When the try variant is used, panics and contract errors are caught and molded into a Result<Result<_,_>, Result<_,_>> developers can assert on. Developers in tests can then assert did the contract:

1. Succeed and return the expected type, Ok(Ok(_))
2. Error and return an expected contract error type as defined by a contracterror enum, Err(Ok(_))
3. Succeed and return an unexpected type, Ok(Err(_))
4. Error and return an abort (panic), or system / host error, or a contract error not included in the contracterror enum, Err(Err(_))

Known limitations

As far as I can tell the purposes of fuzz_catch_panic can be served by the Env try_invoke and the generated contract client try_ functions, but I'd be interested to hear from @brson to confirm if I'm missing any case where we'd want to keep fuzz_catch_panic.

Docs

The stellar-docs need updating as well.