do not ask to inherit __call__ but call
expose some transformers at higher level
expose soem exporter at higher level
allow to pass a resource dict with notebook

only availlable with from_notebook_note
make no sens otherwise
fix filters documentation.

Docstring was stating list instead of dict.

add dynamic list of default filter in Class docstring
Merge pull request #168 from Carreau/some-changes

Some changes

 - Import some stuff at higher level to have cleaner API.
 - Allow resource dict to be passed with from_notebook_node
 - Doc fixes.
 - change (backward compatible) api for Transformer, create dummy call() method without dunder. Allows simple logics when inheriting ActivatableTransformer.