Continuing my tour of the howtos, here's a patch making many of the changes discussed here and on issue13997.  Changes made:

* state that python3 source encoding is UTF-8, and give examples

* mention surrogateescape in the 'tips and tricks' section, and backslashreplace in the "Python's Unicode Support" section.

* default filesystem encoding is now UTF-8, not ascii.

* link to Nick Coghlan's and Ned Batchelder's notes/presentations.

* remove revision history

* remove usage of "I think", "I'm not going to", etc.

* update acks section

Things I did *not* do, though they were suggested:

* Move tip "Software should only work with Unicode strings internally" from the last section to somewhere earlier and more prominent.  Perhaps it could go somewhere in the "Python's Unicode Support" section.

* mention codecs.StreamRecoder and StreamReaderWriter (I could put this in 'tips and tricks').

* Examples should be properly marked up to allow sphinx to run them and check the output.  (May not be possible.)

* mention unicode support in re module

* clarify some more terms (e.g. codepoints, code units, characters, possibly scalar values etc.) -- I don't see why they matter, since we don't use them.