BF + ENH: psychopy.iohub AnalogInput Device

ENH: Added analog_input example to iohub_extended demos.

BF: cleaned up some debugging print in the AnalogInput implementations

BF: Removed reference to `ioHub` added to the copy of LabJackPython
within the iohub device folder during some debugging at some point that
was never removed.
Merge branch 'master' of git://github.com/psychopy/psychopy
BF + ENH: NumPyRingBuffer related

ENH: Added numpy_ringbuffer.py example to iohub_basic.

ENH: Added example to iohub docs.

BF: Fixed crashes related to getting values from ring buffer using slice
notation.