Recurse Center 22: tealeaves refactored

Today I finished a big push of work on tealeaves and got the code fully cleaned up and merged to master and all the tests passing again. When I introduced nom_pem last week things destabilized and it took a while to shake all that out. I'm about ready to start adding some linter style rules like making sure the filesystem permissions on your private keys are restrictive.

I also worked a bit more on pgexercises this afternoon but they really are just exercises with nothing to actually teach you the SQL you need, so I switched back to some Khan Academy tutorials I had worked on about 2 years ago.