Update .travis.yml
added setter for customizing authn method for svc defs
Duo authentication sample - initial commit

This is work in progress. This commit contains the Duo integration code
provided by Duo on GitHub.
Duo authentication work in progress...
Implementation of Duo security 2fa subflow
Duo subflow setup documentation
Typo
Text polishing
Added how to trigger
Merge branch 'issue#81' of github.com:Unicon/cas-mfa into issue#81