Fine-tune ruleset output by type

[trevorld]

• Currently we support is_pamphlet to distinguish between save_ruleset() and save_pamphlet(). But now we also have save_pocketmod() and may also be concerned about "chapter" variants as well.
• May want a single variable with more information or perhaps more variables so we can fine tune output.
• At extreme we may want to allow separate knitr templates by type?