Error handlers for Perceval iterators

[jgbarah]

Request:

Add a new option, when instantiating a Perceval iterator, to specify an error handler. This could be done similar to the errors parameter in codecs.

I would implement at least "strict" (which would always raise the exception, as it does now), "ignore" (which would ignore the item causing the exception, and go on with the next one) and maybe "logging" (which would use the logging module to log the problem, and then go on as with ignore).

Rationale:

• Now, when some exception happens while a Perceval iterator is working, in some cases it is difficult to catch it. That can happen if for some the exception thrown cannot be caught in the calling environment.
• In some other cases, having some error handling policy easily specified is just convenient.