Add some sections on time zone operations.
Fix range.points()

I believe the desire here was to have point range generation without comparisons. While
that may be possible, the method was broken for Months.
Tweak a bit.

Change an example that showed instantiation in a way that users should not use.
Remove some quoted bits.
Make some examples consistent with the surrounding wording.
Expand zone tests and make Zone.slice() reasonable.