RFC: 0079 CDK v2.0

Proposal detailing a new major version of aws-cdk. Lays out the plan for
rolling out the release and continuity for support of current v1
modules.

**Note** Lets talk about issues marked as "More info needed" to decide
if they should be included or not. I didn't quite understand what they
were or why they required incurring breaking changes.

Related to: #79