Updates to ReleaseNotes
Refactoring of test runner and travis support.

 - Now use py.test as testrunner and not nose
 - Added support for tox to test all python versions locally and in travis build
 - Added tox to dev-requirements.txt
Major updates to README.md
Change long_description to include both README.md and ReleaseNotes.rst in setup.py
Code cleanup
New make target 'cleantox' and 'cleanpy'
Add missing file to MANIFEST.in
Added gschmottlach-xse to authors file because of alot of testing of pykwalify
Added dependencies to tox.ini because they are not installed automatically when installed inside a tox env
Fixes to Makefile
Regression: min, max, mix_ex, max_ex did not validate correctly...
Refactoring of keyword 'length'

 - Keyword 'length' is now removed from the schema and is replaced by range that can handle all cases
 - Updated tests that broke after this change
 - Keyword 'range' now checks min, max, min_ex, max_ex if the keys are integers
Add coveralls support