Replace Override.simple with Override.create

This pull request:
1) Renames Override.simple to Override.create
2) Adds support for the missing features that the override functions needed (returning longs and using the context).
3) Ports all the override functions to use Override.create
I wanted to have always the same format for all natives/overrides, to avoid problems (all the async natives need ctx to call resume) and to simplify the transition