This change started out as simply updating the existing inmemory driver to
implement the new Stat call. After struggling with the map based
implementation, it has been refactored to be a tree-based implementation.
This process has exposed a few missing error cases in the StorageDriver API
that should be addressed in the coming weeks.
This change brings the storagedriver API in line with the Go standard library's
use of int64 for offsets. The main benefit is simplicity in interfacing with
the io library reducing the number of type conversions in simple code.
Fixes/tests listing for keys beginning with "/"
No longer extraneously wraps Closers in ioutil.NopClosers
Uses omitempty for all ipc struct type fields
