This PR implements json_pretty. At the moment, support for jsonb is
being added, so this function suffers from the same limitations as in
json(x). Also, I have not found a way to implement the same conversion
of Blob -> String that SQLite does. From my own experimentation, I
believe SQLite converts blobs to a lossy ascii representation, but I
would appreciate some help on this.
Closes#860
2d9a54ccba