This is the commit where I admit that having more than one input/output
format for readers and writers was complicating the code too much for a
very small gain, and that it would be easier to only have one way to do
it.
So such way is now:
- Returning (or yielding) a dict if you have key-value type collections.
- Returning (or yielding) a tuple if you have a list-type collection.
- Returning (or yielding) something else otherwise, which will continue
to work like the old "arg0" format.
IOFORMAT options has been removed in favour of a RemovedOption, which
will complain if you're still trying to set it to anything else than the
one value allowed.
