Adding 'get' command to the CLI, to view a single variable.

This enables the user to type "get variablename" in the CLI, which then shows the value of that variable (or a message saying "Variable 'variablename' not found").
This is easier for the user when they just want to see a single variable, instead of typing 'dump' and then having to parse a big long list of data.  It is also more intuitive than typing 'set variablename', as this feels unsafe.
Re-use existing code to show all matching cli commands for 'get' instead of exact match.

e.g.  'get deadband' will show all varialbles with the word 'deadband' in it.  exact match only required when setting variables.
Merge branch 'nebbian-feature-cli-get'