[Bf-python] API consistency

[Michel Selten]

Hi again,

Hrm, I did more mailing than coding today :/
Anyway, here's an idea of updating the API between Blender versions:

2.28 comes out - 2.23 & 2.25 compatible API.
2.29 comes out - some additions, and probably some problems in the API.
     We add a message to the functions or variables that we want to
     change. This message is then displayed to the user and warns him to
     use another function and that this function will be removed in the
     next version (2.30).
2.30 comes out - some additions, remove the functions/variables in the
     API that we have warned will be removed. Repeat the process.

Of course this shouldn't happen every release. But this gives room for
updating the API to a level where we think is perfect.

Ideas?

With regards,
	Michel