elyses-analytic-enchantments concept exercise

[colinleach]

First exercise for the vector-filtering concept. I'm a bit conflicted about the concept name: filtering is probably clearer for a general audience, subsetting is maybe more technically correct. I've seen both used in R textbooks.

[colinleach]

Apparently, only one exercise per concept can be a concept exercise, any others have to be practice exercises. We'll need to pick either this or bird-watcher #267.