Add Lucene and commons-codec dependencies

Lucene is used for indexing objects such as Twitter statuses. The codecs
are used for base64 encoding/decoding the serialized objects to store
them in the index.
Add common index definitions

Includes common utilities and base classes for working with Lucene
indexes and converting Scala objects to/from Lucene Documents for
indexing.
Add support for writing objects to Lucene
Add support for reading objects from Lucene
Add support for writing Status objects to Lucene
Add apps for working with Status indexes

Includes several objects with main methods to collect tweets from
Twitter's sample stream, filter them, and index them. Also includes
StatusSearcher to search a status index from the command line.
Add tshrdlu.twitter.index package documentation
Mention TSHRDLU_INDEX_DIR environment variable
Merge pull request #2 from njwilson/tweet-index

Support for indexing tweets (and other objects) with Lucene