overhaul dev guide indices, titles, tags

[napcs]

• Change Feature Guide to developer guide
• Get titles consistent - drop "feature guide" and "temporal" from pages, normalize the rest of the titles.
• Combine Python Cancellation and Interrupting Workflows pages into one page like the other gudies
• Update tags where appropriate

[fairlydurable]

Pass was not deep: trying to find user-facing errors or pain points in updated material.

Pulled out diffs and ran through spell checker and grammar checker.

Then did visual inspection of files, much of which was rote.

[jsundai]

LGTM. This looks fantastic!