Stage 2-6: Initial entry points proposal #262

For the Stage 2-6 case involving initial entry points (node file, --eval, STDIN, etc.), I’ve prepared a proposal that builds off of our current implementation:
https://github.com/GeoffreyBooth/node-esm-entry-points-proposal

Feedback welcome as issues in that repo please. Also please note that all names of things are subject to change as the process goes on, and especially in Stage 4 when we get user feedback. All names should be considered placeholders.