MNT: refactor subscriptions (ref issue 21)
MNT: Subscriptions -> OphydObject (ew)
MNT: move things around
MNT: areadetectors are ophydobjects; areadetector property name fix
MNT: ad example fix
MNT: adsignal name fix
Merge pull request #24 from NSLS-II/callback_fix

Callback fix (etc.)