This change separates the metadata specification from the targets doc,
since they are both meant to be consumable independent of one another
and will evolve at their own paces.
This sketches out some more details in the Metadata format, in addition to
starting to articulate what the AWS IaaS provider looks like. Sadly, more
questions than answers, but it's good to have the placeholders...
Simple developer scenarios can be done solely in terms of Stacks. However, to
support more sophisticated cases -- where multiplexing many Stacks onto a shared
set of resources is preferred (for cost savings, provisioning time savings,
control, etc) -- we need to introduce the concept of a Cluster. Each Cluster has
a fixed combination of IaaS/CaaS provider, decided at provisioning time.
This just contains primarily scaffolding, however lays out a general direction
and table of contents for the metadata specification document (marapongo/mu#1).
