Divmod Lupy 0.1.5.5

A minor release with mainly a bug fix in the indexer.Index wrapper.

Changes:
Changed default mergeFactor from 9 to 20 for better performance
Fixed the example in simple.py to use a Keyword for filename, instead of
stored, instead of a tokenized and stored Text field.
Tidied up SegmentInfos and FieldInfos to be more Pythonic.
Call close() on open searcher in indexer.Index.setupIndexer.