like cmap, or glyf or OTL tables, we need to respect lazy=False flag and decompile everything upfront, also we want to add an ensureDecompiled method (called by TTFont.ensureDecompiled) to allow loading everything in one go even when a font had been opened lazily.
* 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
