Merge branch 'release/1.3.0' into develop
Post Release: Version 1.3.0 -> 1.3.1dev.
Use ZenEventClasses instead of numeric constant.

Incorporated from changes made by Bunyk on the wiki.
Support callables in proxy_attributes.
Merge pull request #3 from zenoss/feature/callableAttributes

Please review branch feature/callableAttributes
Release: Version 1.3.1dev -> 1.4.0.
Release: Document 1.4.0 changes.
Finished release 1.4.0.