'''
/Volumes/Kindle/system/vocabulary/vocab.db
bookinfo = { 'book_key': {
            'bookname':'bookname_xxx',
            'authors':'author_xxx'},}
words = { 'word_id': {
            'word':'梅花鹿',
            'category':0,
            'lang':'zh' },}
lookups = {'id':{'word_key':'zh:当',
            'book_key':'iCR!8Z2VQD36EH0HN6FDJN9R8S1P94Z5',
            'pos':'377816',
            'usage':'xxxx',
            'timestamp':'1571540228933'},}
'''

table: BOOK_INFO
  id         - book key, CR!NYRVJ9BT315PKFRS9B9KVB0XF213:6F1EB741
  asin       x
  guid       x
  lang       x zh/en
  title      - bookname
  authors    - author

table: LOOKUPS
  id         x lookups key, CR!NYRVJ9BT315PKFRS9B9KVB0XF213:6F1EB741:xxx
  word_key   - zh:当
  book_key   - book key, like CR!NYRVJ9BT315PKFRS9B9KVB0XF213:6F1EB741
  dict_key   x
  pos        - position, like AYkJAAAAAAAA:28781, 115907
  usage      - usage
  timestamp  - 1566738399454

table: WORDS
  id         - zh:当
  word       x 当
  stem       x
  lang       - zh/en
  category   - 0 learning, 100 mastered
  timestamp  x 1591141963703
  profileid  x

word_id -> lookups_id