use the new doctrine compiler pass to map the model classes directly
deprecate persistence specific classes
adjust to factory method
re-adding empty mapping files to keep BC compatibility
add support for mongo
do not have a fatal error if doctrine bridge is too old
adjust to https://github.com/symfony/symfony/pull/7755
add legacy symfony support
add support for couchdb
updated documentation
added upgrade instructions
put #1113 into this PR
add deprecated errors to constructors, fix Upgrade.md
Merge pull request #1081 from dbu/map-models

use the new doctrine compiler pass to map the model classes directly