Work with Sergio González adding Javadoc to SiteMembershipPolicy. We'll use Javadoc for this class as the basis for Javadoc on the the other Membership Policy interfaces. Having them documented will help developers build custom policies.
pull request: https://github.com/jhinkey/liferay-portal/pull/15
Sergio's commit has some of the Javadoc. We are deriving the rest from notes he sent via email.