Added significant amounts of SCPI 1999 support. Still lots to go.
Started work on ThorLabs PM100USB support. #11
Mostly minor doc improvements.
Copied rigolds1000.py into tekdpo70000.py and changed some names. Nothing is functional yet.
Moved bool_property and enum_property to util_fcns
Added documentation to bool and enum _properties
Added an abstract electrometer class and the untested start to a concrete implementation of one such device.
Made a slough of small changes to get keithley6514 to import without error.
Ironed out keithley 6514 class

Fixed a bunch of bugs, made more features work, and provided a working
example.
Added the unitful_property helper function to util_fns
Added the string_property helper function to util_fns
Added unitless_property helper function to util_fcns
Filled in the Math and Channel classes
Added a readonly option to the various property functions
Added properties from the horizontal and acquisition sections.
Started dev guide.
Added docs of util_fns.
Updated TOC.
Added more docs to util_fns.
Merge branch 'dev' into feature-unittest

Conflicts:
	python/src/instruments/util_fns.py