Add @keywords #154
Description
per suggestion by @dajmcdon:
To view “all possible endpoints”, we could add @Keyword tags to each of their documentation files. This has 2 benefits. One is that this can be easily (and quickly) searched. So we could write a small helper, say, available_endpoints(), that would just list them all. If we add more later, we just remember to add the same keyword to the epicall function. The second benefit is that the _pkgdown.yml reference index can contain has_keyword(…), so we don’t need to list all the endpoints individually. Since this (and likely lots of other parts of the documentation) are shared across all signals, we could even extract anything shared to a single doc. I can probably do this as a PR if others think it would be worth having.