* Replaced all from ...py23 import * with explicit name imports, or removed completely when possible.
* Replaced tounicode() with tostr()
* Changed all BytesIO ans StringIO imports to from io import ..., replaced all UnicodeIO with StringIO.
* Replaced all unichr() with chr()
* Misc minor tweaks and fixes
Note UI change : `fonttools varLib.models` now takes prefixed options `-d` or `-l` instead of guessing the intended feature from the number of arguments.
We have a number of command line tools which are somewhat opaque. (varLib.models in particular was very confusing.) This ensures that they all use argparse to have a consistent interface, and all have --help documentation which at least details their parameters, and hopefully therefore gives more of a clue about what they do. Those which use logging have had a command-line logging parameter added.
This adds a `help` verb (and `--help` option) to the `fonttools` command line tool. Submodules will be listed in the help text if they have an importable `main` function with a docstring, and `main`'s docstring will be used as the one-line description for the help text.
