Improving strftime documentation.

Re-ordering the table so similar directives are grouped together, adding
examples, and removing some redundancy in the description of the ``%f``
formatter.
Adding localized examples to strftime documentation.
Correct misleading strftime documentation.

strftime using locale-aware formatting directives will often, but not awlays,
produce UTF-8-encoded Unicode.
Remove Japanese datetime examples
Clarify that strftime's encoding is based on locale
Clean merge
Issue #17701: Improving strftime documentation