Add badgesDirectory option, improved error handling, suppress coverage warnings

[sgb-io]

Resolves #70
Resolves #66 to some degree

• Added the badgesDirectory option to let users configure where the badges go
• Improved some error handling so that users get specific errors but also generic ones (e.g. "option XYZ not supported" in addition to "could not parse your options file"
• Turned off coverage warnings whilst it undergoes a rethink (see Re-consider the role of coverage #58)
• Added an ugly-but-useful verify script. Optional step that helps in local dev - final check before pushing up the work & opening a PR