Access CallError without macros

[That3Percent]

If you need to access CallError (which is used in the signature of register_async_method) the only path to do so is through types::error::CallError. But, the types crate is only available if the macros feature is included.

This is undesirable. Instead, CallError should be re-exported from the http_server crate, or the types crate should be available when the server feature is specified.

[dvdplm]

I agree and have had the exact same thought.