Improve pt-br wordlist (#63)

Wordlist in pt-br was first introduced in 7743ed55. The differences to
this one are:

  - 9-characters words are introduced.
  - suffixes removal is made after accounting for popularity.
  - less frequent words that differ only in the last character are
    removed.

The current pt-br wordlist was generated as follows:

  1. Download a dump of portuguese Wikipedia pages, process all pages
     and determine the frequency of each word.
  2. Start from /usr/share/dict/brazilian and filter out:
       - words not matching /^[a-z]+$/,
       - words shorter than 4 characters, and
       - words longer than 9 characters.
  3. Sort remaining words using pt Wikipedia frequencies.
  4. Take the top 30K words (just because after filtering we still get
     roughly the amount we need).
  5. Filter out:
       - all words that are a suffix of any other word in the list.
       - less frequent words that differ only by the last character.
  6. Take the 7776 most frequent words.

No further curation was made.