Rename decl_module to decl_dispatch

* Renamed all instances of `decl_module` to `decl_dispatch`
* added `$crate::` to all the macro uses so that it is automatically expored
* Created a forwarder macro which simply takes any existing usage of `decl_module` and forwards to `decl_dispatch`
* Added a deprecated flag to show a warning when `decl_module` is used