* Make the declaration of fct and it in the constructor Collection,
 instead of adding them from the outside
* Add a function to flatten a list containing collection (solves the
 radioob search crash)
* Better display of collections in the "ls" command (and display both id
 and title)
* The "cd" command goes to the root of the path (like the UNIX cd)
* Move the Video object of canalplus in a correct path
* Make Collection iterable
* Add comments to CapCollection
* Cache the result of fct in a Collection; it is only called once
* CollectionNotFound errors can be more explicit by providing a path
* Require utf-8 in collection paths
* Code cleanups

Signed-off-by: Romain Bignon <romain@peerfuse.org>

Because unsurprisingly pastealacon has silly restrictions.

For pastealacon, it is used to check for encoding compatibility.

This allowed to fix a crash when parsing descriptions with invalid
unicode (KickAss is quite horrible it seems).

A new attribute, filename, has been added. It is the recommended
filename of the .torrent file, and should simplify downloading files when
it will be supported by weboorents.

The usage text/tail was useless, lxml supports text_content() for HTML,
which is much simpler.

Basic support in pastoob added (there is no way yet to change the
default options).
Backends support the "public/private" requirement.

And fix the capability.

It's a huge copy-paste of CapVideo, and will have to be factorized ASAP,
though it's going to require more work and thinking, and maybe CapPath.

It is able to get a paste, and post a new one.
Only the contents and title fields are supported for now.