Merge pull request #10 from adulau/master

Whoosh requirements added for Indexer modules
Return the number of indexed documents
-l added -> dumping all terms indexed
Indexer: Some index statistics added

usage: indexer_lookup.py [-h] [-q Q] [-n] [-t] [-l]

Fulltext search for AIL

optional arguments:
  -h, --help  show this help message and exit
  -q Q        query to lookup (one or more)
  -n          return number of indexed documents
  -t          dump top 500 terms
  -l          dump all terms encountered in indexed documents