The errors generated by `RESPTokenDecodable.init(fromRESP)` need improved

Currently most of the `RESPTokenDecodable.init(fromRESP)` implementations throw a `RESPParsingError` as there is no alternative. In the context of decoding a RESPToken this error is pretty useless. We need a decoding error type which provides more information, but without additional cost to the decoding process. 