Fix numerous issues with the tokenizer for twitter

1. Re-use the same objects for each tweet, instead of recreating for
every new tweet.

2. Lacking lucense token types, we were stemming acronyms, in some
cases disasterously so, e.g. "IEDs" --> "i"

3. Twitters URL recogniser is pretty feeble, it seems to rely on
http:// being there. Added a fairly basic URL regexp approach that
inserts http://s where it thinks it makes sense so we can extract these

[3 was pretty bad: lots of URL shrapnel was being processed as normal
words, and due to shortening services the number of such "words" was in
the millions]
Add @Override annotations where appropriate
Updated DateStats to print out counts of hashtags, smileys, addressees, URLs and words