automated changes by python-modernize (without fix_unicode for now)
setup.py: require 'six', add classifiers for 2.6 and 2.7
manual py3 compat fixes
py3 compat: fix str/unicode for exception base class
py3 compat: fix base64_(en|de)code, int_to_bytes / bytes_to_int

also be more precise in docstrings about datatypes
do not use %s%s to concatenate bytestrings (doesn't work with py3), cleanup exception msgs
fix default salt bug in make_signer
py3 compat: manually fix unicode/bytes
Removed six and fixed support for Python 3 stdlib JSON.
Fundamentally changed unicode/byte dumping behavior for Python 3
Current version is 0.19
Added travis.yml
Added changelog entry
Updated upload-docs command
Fixed a docstring and introduced a use of want_bytes
Use the stdlib digest_compare if available
Fixed a bug in Python 2.6
This is 0.20