Update how to deprecate code

[fredjaya]

Need to clarify:

• [ ] The differences between deprecating and discontinuing code
• [ ] Also how to deprecate arguments

[GavinHuttley]

to discontinue is to delete a module, function, method, or argument

to deprecate means to rename one of the above (which can include relocating to a new location)

But I'd check whether my definitions are consistent with what the Python community thinks those terms mean