PSA Create dedicated error handling section

[jafingerhut]

Creating this issue in case Calin's suggestion at this linked comment is something we want to pursue:
#489 (comment)

Copying the relevant text here:

We have throughout the document the following sentences:

A comment saying “recommended to log error” is not a requirement, but a recommendation, that a PSA implementation should maintain a counter that counts the number of times this error occurs.

These apply to parser errors and other controls. I propose that we should have a standalone (sub)section that deals with error handling, in which we also show the example of parse errors.