doc URLs refer to hydra, not github

[matthewhammer]

Until now, I was storing auto-generated AS documentation on github, and this was bad because:

1. I was generating and committing this documentation "by hand" (invoking a script each time I made change)
2. github was polluted with machine-generated output from this process
3. doc URLs were hard-coded into the AS source's comments, and were quite long

This PR addresses each point above, by

• Using a "variable" named $DOCURL that gets expanded automatically via the python scripts
• Uniformly referring to documentation on hydra, not github

Also, this PR has some other minor cleanup to the documentation.