Reverted changes pertaining to holding DocumentFeature-s in a shelf because populating the shelf at startup takes too long (even though using it later is faster)
Removed unnecessary information returned by PrecomputedSimilaritiesVectorSource.get_nearest_neighbours to speed it up by an order of magnitude. This breaks compatibility between its API and that of CompositeVectorSource, which is ok as the latt
    (cherry picked from commit e54912b)
Updated unit test of Token (NER tag not used in __eq__, __lt__,... methods any more). This is a cherry pick from a few days ago.
Merge remote-tracking branch 'origin/master'

Conflicts:
	discoutils/tests/test_io_utils.py