Add header for deploy start message including start time and user@host
that started the deployment and a list of the target profiles being
processed.
Add interactive prompt confirmation for each profile being deployed.
Moved deploy confirmation prompt to before executing pre-deployment
local commands and fixed prompt issues when a boolean prompt received
invalid data.
Add and document cross-referencing variables in deploy descriptor
documents.
Add support for env_ prefixed variables declared in the env object.

Variable references in these properties do not support json_ document
cross references.