Stats: Added verbose option to segments api, with full ram tree as first additional element per segment

This commit adds a verbose flag to the _segments api.  Currently the
only additional information returned when set to true is the full
ram tree from lucene for each segment.

Note: I added the ramTree as a public member on the `Segment` class.  This class has a mix of struct like members and some that have getters.  It really should be cleaned up, but here I tried to follow what seemed like the most common pattern there.
Maybe we can add a code comment about why these simple recursive impls are ok, since tree depth should be something tiny like 5 or 6.