Tidying up! Add doctests

[sneakers-the-rat]

Love the reorganization in #48

Noticed that a bunch of the pages were not showing up in the toctree, so i went to add them, and i noticed that there were an avalanche of warnings that probably makes it hard to tell what is actually a meaningful warning and what is just noise, so i also fixed all those.

Not a contentful PR, but things to note:

• I switched the docs build to docs-test so we can help ourselves out by alerting us to when links are broken/etc. and fix them as we go. we can disable that if people find it annoying, i personally find it helpful because i always forget to check before i push.
• I renamed the python-conditionals link target to just conditionals because there was an ambiguity error (i assume since the file is named python-conditionals.md)
• I added raises-exceptions tags to all the python notebook cells that were failing, most of them you had explicitly written that they should fail around them, but there were some where i wasn't sure, so if there are any i marked here that aren't supposed to fail then those probs need to be fixed :)

[lwasser]

oh gosh - @sneakers-the-rat THANK YOU for this! i saw all of the warnings but i haven't had time to focus on them. this is awesome. thank you! also the doc-test idea is a great one.

[sneakers-the-rat]

also feel free to ignore the errors if you're getting into crunch time prepping for the workshop but you already know that ;)