Game annotation app for iOS

I've been looking for an app that would allow me to annotate games by adding nested variations and numeric annotation glyphs (eg. !, ?, N), and also allow me to run an engine to help analyze.  The best I've found so far is Giordano Vicoli's Chess_Studio.

https://itunes.apple.com/en/app/chess-studio/id684224545?mt=8

It doesn't have an opening tree or keys, so it's kind of hard to search for specific positions, but it does let you search by player or ECO code.