* deep changes in libwaku to adap to nim-ffi
* start using ffi pragma in library
* update some binding examples
* add missing declare_lib.nim file
* properly rename api files in library folder
This change is needed so that interoperability with other languages becomes simpler.
Particularly, this simplification is needed from the Python point of view,
where it is tricky to pass a void** as a parameter to an FFI function.
