Before I used to have the different types of inputs/outputs seperated into
lists inside the scan op. I've made a more generic approach, where there is
a simple list of all inputs/outputs for scan.

Construct an instance of the Scan Op and apply it to inputs

The distinction between different types of inputs/outputs is not really
necessary anymore, so in order to simplify the code I just create a single
list of all inputs

I keep track of the original shared variables, plus remove the distinction
between outer and inner since is not needed anymore.

I do not really use ``states_and_outputs_info`` list anywhere after that
point. I will use mintaps however. Normally I would have to feel both lists
with the defaul, but since I'm not using the first one anymore, I'll just
fill the second one

I will use ``cond`` as ``as_repeatUntil`` because both variables have the
same semantics

Note : some of them are copies of the ones in the old scan

This is a clone of the documentation already existend from the old scan.

Minor stuff

Updated NEWS.txt following scan change.

Fixed some tests

Temporary fix to a known bug for scan.

Added warning about sigmoid identification bug

Fix scan crash in recent change.

The code seems fine.,