Add support for Agilent 8156A optical attenuator
Proper error query for Agilent 8156A
Update copyright dates
Add support for Agilent InfiniiVision 6000A series
Agilent Infiniium 90000 series only supports DC coupling
TIFF save for InfiniiVision scopes is only for graticule data, not for screenshots
Invalidate attributes when reloading stored configuration
Add documentation and vertical scale property
Add documentation and differential/common mode display properties to Agilent Infiniium 90000 series driver
Fixed 50 ohm input impedance in Agilent Infiniium 90000 series
Add value storage for new properties in Agilent Infiniium 90000 series
Add display.vectors property to all Agilent scopes
Add support for color grade persistance to Agilent 90000 series
Add system.display_string method to all Agilent scopes
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Add system.display_string method to all Agilent scopes
  Add support for color grade persistance to Agilent 90000 series
  Add display.vectors property to all Agilent scopes
  Add value storage for new properties in Agilent Infiniium 90000 series
  Fixed 50 ohm input impedance in Agilent Infiniium 90000 series
  Add documentation and differential/common mode display properties to Agilent Infiniium 90000 series driver
  Add documentation and vertical scale property
  Invalidate attributes when reloading stored configuration
  TIFF save for InfiniiVision scopes is only for graticule data, not for screenshots
  Agilent Infiniium 90000 series only supports DC coupling
  Add support for Agilent InfiniiVision 6000A series
  Update copyright dates
  Proper error query for Agilent 8156A
  Add support for Agilent 8156A optical attenuator
Replace hole values with NaN for Agilent scopes
Add documentation to scope base class
Sort attribute lists returned by help and doc methods
Add scope class to sphinx documentation
Add measurement_function values to scope documentation