Add dynamicProperty/normalization info and polish.

[knutnergaard]

• Adds new section explaining dynamicProperty and how it handles normalization.
• Breaks down the main code block and accompanying documentation into smaller sections for clarification.
• Modifies the language slightly in certain places.
• Adds links, cross references and other markup.

[knutnergaard]

As with #836, I have no idea why mypy fails here, given that the edits are irrelevant.

[knutnergaard]

@benkiel Can you merge this? Unfortunately I committed it straight to my fork's v1 clone, so further contributions to this branch will be a bit awkward otherwise.