Pass a copy of the control frame buffer to ping/pong callbacks (#116)

• Pass a copy of the control frame buffer to callbacks

• Add back old API

Since the new and old methods are only overloads and share the same name, the ‘renamed’ parameter of the deprecation warning doesn’t help.

• Allow specifying payload when sending ping

• Remove default value in favor of method forwarding

This preserves the signature of the original method and doesn’t break the API

• Apply suggestions from code review

New APIs should use safe code