[Proposal] Custom parser in recover middleware

The parser of the recover middleware is hard coded. The only issue with this, that most of the log aggregator solutions can't handle that kind of format. As I checked the code `prettyStack` is the actual implementation of the parser inside the recover.go.

**Proposal**

What do you think about to create an interface with a method: `Parse(debugStack []byte, rvr interface{}) ([]byte, error)`, and a singleton pattern like `var stackParser {INTERFACENAME} = prettyStack{}`. After we can use the `stackParser` in the `PrintPrettyStack`. Also adding a function to `SetStackParser({INTERFACENAME})`.

What do you think about? If you like it, I can implement it with a few tests.

The proposal looks like this: https://github.com/PumpkinSeed/chi-recover-proposal/pull/1