#354 Document Depreciated/removed functions

[Michael Beck]

See: http://www.xoops.org/modules/newbb/viewtopic.php?post_id=331604#forumpost331604

What would really help is if the core devs documented two things:
- every function they deprecate when a new release is made (along with a preferred replacement example)
- every function 'removed' (previously deprecated)