Make test/exercises self-documenting and user-facing

[ben-albrecht]

Often, tutorials, workshops, and online exercises will contain code copy/pasted from exercises within test/exercises. Unfortunately, these codes hosted online can go out of date over time, due to changes in the language or the exercises.

A better long-term solution for this would be to clean up the exercises directories and add instructions into local README.md files such that users can be given a more future-proof GitHub link to the exercises directory pinned to a specific release or master, e.g. https://github.com/chapel-lang/chapel/tree/master/test/exercises

[bradcray]

I tried to refine the title to try and capture what I think the intent is: Make test/exercises/ something that, if you were to point an end-user to it, they could navigate it themselves due to good documentation, organization, etc.