work around a crasher when accessing frame.f_restricted
http://bugs.python.org/issue21967
pep-8 fixes
Update and simplify the threading example.
The environment variable PYHEAPDUMP_DIR can be used to define the 
directory for dump files.
Change the sys.except hook handler to catch only
Exception and its subclasses.
Documentation upgrades.
Enhanced the example.
Prepare version 0.2.1