encodings.py: excluded are not just binary

Update the comment to better describe why base64, undefined, etc are
being excluded
encodings.py: Add wrapping

Fold long lines to 76 characters, in order to aid readability e.g.
when viewing the README.md page on GitHuh (whose HTML sucks in this
particular respect -- there should be a way to read long lines in
preformatted blocks).

Turning off wrapping currently requires a code change, sorry.
encodings.py: Experimentally output Unicode LTR

Attempting to fix bidi issues by explicitly printing a LTR marker
after the generated glyph.  However, this does not seem to do anything
useful at least with Emacs, and I'm pessimistic about Firefox.
README.md: refresh generated content

Encoding lists are sorted, aliases are pruned, each line of output
has an LTR marker (which however might not actually do anything
useful).  All overlong lines are wrapped for legibility.