Update docs for 0.15.x

[Technologicat]

Perpetual moved TODO (see #66):

• Check the tone of our criticisms of Python, that we don't come down too harshly on it - for the most part, the language is excellent. (If it wasn't, it wouldn't have made sense to build this whole thing - maybe we should mention that.) Especially the focus on readability. The vertical-space-saving indentation-sensitive surface syntax is nice minor detail, too. As is the general with protocol.
• Consider switching away from Title Case in Documentation Headings, in favor of Just capitalize the first word, to increase readability. It's a feature of capital letters to catch the eye and stop scanning; let's use that effectively.
• Ping aisha-w about proofreading any new docs, if they're still interested.