Separate method for testing purposes (and so Data doesn't need to be constructed by callers).

Separate method for testing purposes.

Separate method for use by modifiers (shortcut.go, cache.go, etc.).

ProcessGraphExecution processes the provided graph.

ProcessGraphUse processes the usage for provided graph.

ProcessNewGraphUse processes the usage for provided graph.

ProcessOrComplete checks if the provided processor is a `Node` or just a `Processor` and traverses the subgraph or completes the processor accordingly.

ProcessOrExecute checks if the provided processor is a `Node` or just a `Processor` and traverses the subgraph or executes the processor accordingly.

ProcessOrUsage checks if the provided `Processor` is a `command.Node` or just a `Processor` and traverses the subgraph or executes the processor accordingly.

ShowUsageAfterError generates the usage doc for the provided `Node`.

Use constructs a `command.Usage` object from the root `command.Node` of a command graph.