Add warnings instead of outright removing function

[hmaarrfk]

In addressing #1599 (comment) (thank you)

a method close was removed.

However, i'm seeing many bug reports about this having unintended effects downstream.

imageio/imageio#1111 is one for example.

It would be good if instead of outright removals, warnings are added such as

from warnings import warn

def foo():
    warn("the function foo was deprecated in 14.0.0. Please do the following instead .....", stacklevel=2)

to help libraries transition in a smooth way.