Update Test comments as seen in http://tools.ietf.org/rfcdiff?url2=rfc5869
Allow salt to be None in test title
Add test case number 7 from http://tools.ietf.org/html/rfc5869
Simplify code
Fix whitespace and punctuation
Add hash algorithm to TestCase's __str__ output
Merge branch 'master' of https://github.com/webmaster128/python-hkdf into merge-PR1
Fix style and simplify conditionals.
Move byte pretty printing into function

- Add function to prepare a shortened hex unicode from a byte sequence.
- Begin switch to explicit unicodes and the binascii hex functions in case
  Python 3 ever happens.