Remove __getitem__/__setitem__ accessors

These are oversimplified and undocumented

Change-Id: Idbea320c9ea601a8a26ef0fa6d657cd748b3ebfd
Rename incr/decr to counter

This is a breaking change. Docs still need to be updated accordingly

Change-Id: Iedd6733ff77c0bbf05a9c363cd0e53a0004dc5b6