Support favorites

[stilist]

• favorites.getPublicList (docs): User’s publicly-accessible favorites.
• favorites.getList (docs): Full list of a user’s favorites, including non-public ones. r
• favorites.add (docs): Add a photo to user’s favorites. w+
• favorites.remove (docs): Remove photo from user’s favorites. w+

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getList and getPublicList accept per_page (0..500; default 100) and page (n; default 1) parameters for use with large collections of favorites. The <photos> element of the XML response includes a pages attribute indicating how many calls are needed to collect all the favorites for the given per_page, as well as a total attribute that states how many favorites the user has.

For the user’s convenience, I suggest an optional argument along the lines of n_favorites that will automatically make the required number of calls and assemble a unified list. (A more complicated but full-featured alternative would be start and end arguments.)