* schoolutils/grading/ui.py: use print_function for python3 compatibility
schoolutils{config/__init__.py, grading/ui.py}: use dict.items(), not iteritems()
* schoolutils/grading/ui.py: rename raw_input to input for python 3 support
* schoolutils/reporting/reports.py: rename cStringIO to io; pass unicode to StringIO.write
* docs/project.org: notes on Py3 support status
* schoolutils/reporting/reports.py: use list comp instead of filter()
* docs/project.org: more notes on Py3 support
* docs/project.org: TODO updates based on feedback
* schoolutils/grading/calculator_helpers.py: map, filter updates for python 3 support
* schoolutils/grading/ui.py: py 3 support: explicit encoding when writing grade report
* schoolutils/grading/ui.py: py 3 support: map, filter fixes
* schoolutils/grading/ui.py: fix indentation issue (thanks, pylint)
* docs/project.org: Python 3 support notes, cont.
Merge branch 'py3' into grader_features

Initial changes to support Python 3.  This is the low-hanging fruit:
print_function, map, filter, etc.  Some testing indicates the code now
runs on both 2.6/2.7 and 3.2, though I haven't tested all functions
thoroughly on all versions.

Hopefully this will mean that upgrading to Python 3 in due time will
be painless.  My current plan is to support whatever version is the
system Python in Debian stable.  When Debian fully moves to Python 3,
I will remove 2.x-specific code.  In the meantime, given these
changes, it should be pretty easy to maintain a single codebase
compatible with both 2.x and 3.x.