* 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
Somehow we forgot to replace round -> otRound in arrayTools.calcIntBounds.
This function is used by glyf table to compute the glyphs' bounding boxes.
We already use otRound (aka 'int(math.floor(v + .5))') to round glyph
coordinates upon compiling glyf table. So the use of python3's round
in calcIntBounds was producing inconsistent roundings between the glyph
coordinates and the glyph bbox (sometimes, i.e. only when the glyf table
contains float coordinates, e.g. after instantiating with varLib.mutator).
