Bump version to 2.0.0-M6, upgraded fenix-framework to 2.4.0
Upgraded dependended libraries, dropped commons-codec in favor of guava
API reviewed, several domain methods had their visibility reduced using the new 'protected' keywork of the fenix-framework. UserSession no longer has digest secret, all moved to renderers where they belong.
UserSession no longer part of the public API. Developers will only see User instance from now on. USER_SESSION_ATTRIBUTE dropped in favor of LOGGED_USER_ATTRIBUTE. User is the java.security.Principal
Added documentation