Lazy evaluation

[Andrew-Morozko]

Since we're moving to dynamic schemas all of the parsing is done in our code (right now gohcl decodes the whole struct and its children, whether we need it or not).

This means that we do not need to parse the bodies of the blocks or resolve refs if we don't have to. As far as I understood, the primary goal of this tool is to render a specific document. What if we do it like this:

1. Parse top-level block headers
2. Find the requested document and begin parsing its body
3. Execute plugins, resolve refs, and evaluate blocks when they are needed by the document body