Add compendium with example macros showing how the API can be used

[DC23]

The compendia are stored by Foundry in a binary format that doesn't play nicely with Git. There is a Node CLI tool that converts them to JSON for storage in Git, and a GitHub Action can reverse the process for packaging the compendia into the build artifact. See:

• Discord conversation
• a5e for dnd5e
• Foundry-cli docs