ReSpec build script

[ralfhandl]

• [x] EDITORS.md with guessed lists of current and previous editors
• [x] package.json with dependencies
• [x] scripts/md2html/* build script adjusted from OAS

Preview:

• https://ralfhandl.github.io/OpenAPI-Specification/overlay/v1.0.0.html

[handrews]

@ralfhandl I don't think I've ever made a single contribution to the Overlays spec, so I should not be on the 1.0 editors list.

[lornajane]

Can this be used locally? Let's add the instructions in to the contributing file.

I would name all those editors as current editors, both Ron and Darrel did a LOT to get Overlays to this first 1.0 release.

[ralfhandl]

Added CONTRIBUTING.md with local build instructions