Abstract settings from IPC-compliant scripts

[evanshultz]

#422 includes #ToDo comments about where to capture generic settings for 'paste_radius_ratio' and 'paste_maximum_radius' in ipc_gullwing_generator.py and ipc_noLead_generator.py.

A few other lines that could perhaps be abstracted in both scripts are:

DEFAULT_PASTE_COVERAGE = 0.65
DEFAULT_VIA_PASTE_CLEARANCE = 0.15
DEFAULT_MIN_ANNULAR_RING = 0.15

The no-lead generator also includes this:

SILK_MIN_LEN = 0.1

It seems to me that https://github.com/pointhi/kicad-footprint-generator/blob/master/scripts/Packages/package_config_KLCv3.yaml would be a good place and it's already pulled into the footprint generator file.

https://github.com/pointhi/kicad-footprint-generator/blob/master/scripts/Packages/ipc_definitions.yaml may also be a fine place to store the rounded rectangle pad requirements as they are IPC parameters.

Naturally, the PR mentioned above will need to be merged first or else a PR submitted which is branched from Rene's branch.