Add new mission/talk effect u_learn_recipe

[ralreegorganon]

Summary

SUMMARY: Features "Add new mission/talk effect u_learn_recipe"

Purpose of change

This adds a new effect for usage in dialogues and missions, u_learn_recipe which will teach the player the specified recipe. It also has a counterpart condition to check whether a recipe is memorized, u_know_recipe.

Describe the solution

I followed the existing patterns for effects and condition here. The only special things to note are that a recipe is only considered known by the condition if it's memorized--having a book with the recipe on hand is insufficient, and the recipe may be learned even if the player has insufficient skill to execute it.

I also added a demonstration mission that uses this feature, where the player is asked to fetch cattail stalks and is then taught how to make cattail jelly. It's not really the focus of these changes--I just wanted to have something exercising the functionality and I feel like we can always use more missions.