Adds diff for differing strings.
Makes diffs work for unicode strings too.
Fixes diff'ing strings in python3.
Automated merge with git+ssh://github.com:CharString/expecter.git
Installs sphynx and stops installaing nose on Travis.

sphinx is needed to build the docs:
https://www.travis-ci.org/garybernhardt/expecter/jobs/4639483/#L31

nose is preinstalled.
http://about.travis-ci.org/docs/user/languages/python/#Pre-installed-packages
test script exits with status 1 on failure