Added a 'help' param to Context

[cb1kenobi]

When displaying help for a command, it only renders the description which is usually a one-liner. An explicit help parameter would allow a command to define multiple paragraphs of text to render above the usage. If help is defined, then the description is not rendered.

[cb1kenobi]

Maybe this could be a hook or something that would allow handlers to render output after the generated help info. This would be useful for examples.

[cb1kenobi]

Fixed by 8dd9880!