version 0.4: minor code changes, debugged database

- The database is built under Python 3.3.2, so it should correctly
  implement Python 3's Unicode tricks, including special handling
  of Greek lowercase letters. (Version 0.3 was supposed to do this
  as well, but apparently, it didn't.)
- `word_frequency` and `iter_wordlist` can be imported from the
  top level.
- The new function `random_words` supplies a string made from
  random words that are sufficiently high in rank order.
A different plan for the top-level word_frequency function.

When, before, I was importing wordfreq.query at the top level, this
created a dependency loop when installing wordfreq.

The new top-level __init__.py provides just a `word_frequency` function,
which imports the real function as needed and calls it. This should
avoid the dependency loop, at the cost of making
`wordfreq.word_frequency` slightly less efficient than
`wordfreq.query.word_frequency`.