Propagate skipkeys parameter to JSON encoder
Add long word hyphenation and text cleanup

- Add git submodules for pyphen and readability;
- Add guess_language package to requirements.txt;
- Add long word hyphenation with pyphen. The maximal word
length is configurable in settings.json. Hyphenation is based on
language guessed with guess_language. TODO: we can do better
here, e.g., by analyzing lang meta from HTML or probably using
Google Translate API on the client;
- On the client side, attempt considering punctuation when calculating
the split point of the current word.