add --importpath (existing|example) option

[mydevpeeps]

Create an option to use an existing marlin root to create the initial JSON file.

Create an option to use an example config to create the initial JSON file.

This is also is a precursor to the effort to automatically pull all marlin example configuration into the repo as JSON examples.

[mydevpeeps]

@p3p has provided a tokeniser that was previously written.. I will take a look and see if I can derive the logic for this to use in the configurator.