Update README.md to fix a broken link

switch to dev_workflow.rst as dev_workflow.md does not exist anymore
Testing python 2.6 in travis.
Fix .travis.yml
Merge pull request #154 from aterrel/travis_2.6

Test python 2.6 on travis
Adding testing driven code documentation
Merge pull request #155 from aterrel/update_dev_doc

Adding testing driven code documentation
Merge pull request #149 from milos-popovic/patch-1

Update README.md to fix a broken link
py26 compat