#DDC-2664 Document new Proxy factory flags usage as of DCOM-210

[Document new Proxy factory flags usage as of DCOM-210](http://www.doctrine-project.org/jira/browse/DDC-2664)
#DDC-2664 Improving and fixing documentation for new Proxy factory flags usage as of DCOM-210
Merge pull request #782 from mnapoli/patch-4

#DDC-2664 Document new Proxy factory flags usage as of DCOM-210