* Refactor of waku.doc.go
Moved out all code from docs.go, placed much of the seemingly misc code into much more closely related files, created a dedicated const file for housing all the package consts.
* Moved doc_test to message_test
* Refactored type collision and check on nil err
* message_test.go fmt
* Implemented whisper/doc.go refactor
* import order change to attempt to please the linter.
* Bug fix on whisper_test.go
I also spotted a load of redundant type casting and fixed some of them
cc8d57752f