Initial spec development/publication process

[gregsdennis]

This is an initial write-up of the SDLC proposal from three weeks ago.

There's more in that discussion that doesn't really go in here

• meta-schema $id values
• that we're disallowing unknown keywords
• features that need to be extracted
• implementation support for experiments

[jdesrosiers]

This looks like a good start. We'll need to flesh out some of the details, but I'd be in favor of merging this as is and make incremental improvements as we decide on more of the details.