This increases the chance of hitting the correct letter when typing a word
that exists in the dictionary, rather than only correct it after the fact.
It is most effective after 2 or 3 letters of a word have been typed and gets
more accurate with more typed letters in the word.
If 2 adjacent letters have similar probabilities of occuring, then there is no
hit correction applied.
First pass at automatically adding new words that the user types and deliberately
accepts.
After typing the word 4 times, the word gets promoted to being valid.
After typing the word 7 times, the word gets added into the UserDictionary and can
be removed from the UserDictionary Settings UI.
Also add a second row of symbols to the period popup.
