Episode 3 fixes from first run-through

[jdangerx]

TODO

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1. turn JSON requests.get() challenge into the example, scrap the challenge
2. break out authentication stuff from the "web APIs = functions" stuff
3. define what remote data is
4. link to what PUDL is
5. mention that remote data takes time
6. better way to show the years
7. research if all read_* methods can read from URL
8. other advantage to URLs is that they're more portable than local paths
9. call back to XML for response.text
10. visual breakdown of function <> endpoint correspondence
11. add documentation for env vars
12. frame up api section with "every API is different, here's the actual skills - learning how to read the docs, learning how to handle error messages, and iteratively poking at the API"
13. consumption challenge that puts "read the docs + learning about error messages" together
14. cut function <> endpoint challenge
15. motivate EIA consumption data
16. motivate EPA facilities data
17. talk about get/post/status/headers when dealing with requests
18. split EPA challenge into multiple questions that mirror the exploration framework
19. tease EIA 923 spreadsheet vs. API difference