Merge branch 'release/0.4.1' into develop
Corrected copyright in docs
Removed trailing white space.
Python 3.x compatibility refactoring. Fixed doctests.
Also run tests under Python 3.
Correct doctests in docstrings
Merge pull request #6

Need to use wrap `url_str` in unicode to get the README doctests to pass
on my Python 2.7 install.  Without this, you get a mix of bytestrings
and unicode strings returned from the accessors.

Conflicts were just doctests.

Conflicts:
	purl/__init__.py
Use tox
Fix unicode doctest issue in Python3

We no longer use the `unicode` function (which doesn't exist in python3)
but instead adjust the README doctest to pass a unicode string which
makes the doctests pass in 2.*.

Doctests do not play nicely with Python3 and unicode and so they are
only useful when testing in python2.*

Fixes bug introduced in 73c1575 as part of #6.
Add travis target to icon in README
Bump version and update CHANGELOG
Ensure version string is a bytestring

Else running 'python setup.py sdist' chokes on a unicode error:
http://stackoverflow.com/questions/12464561/unicodedecodeerror-with-pip
Fixed Python 3 compatibility of 'setup.py'. Helper function 'b' (based on 'six' package) should help with future cases of unicode/bytes string literals).