[DDC-692] Add docs on 2.1 read only entities feature
fix entity manager reference in repository code sample
fix entity manager reference in repository code sample
Add cookbook entry on MySQL Enums.
Merge branch 'master' of github.com:doctrine/orm-documentation
Update section on mixed query and add notes on multiple entities in FROM clause.
Update section on mixed query and add notes on multiple entities in FROM clause. (update paragraph)
Add note box on cascade operations being performed in memory and reference to foreign key /database-level onDelete option for deleting associtions
Changed registerDoctrineTypeMapping('enum', 'varchar'); to registerDoctrineTypeMapping('enum', 'string'); as 'string' is the correct type to map to whereas varchar is only an alias.
Removed '--force' Option for the orrm:schema-tool:create command as this is not available for this command.
Removed another instance of '--force' Option for the orrm:schema-tool:create command as this is not available for this command.
Changed instances of entity manager variable '' to '' for consistency.
Corrected annotation for sample code: moved repositoryClass attribute from @Table to @Entity.
Merged pull request #26 from asartalo/master.

Getting Started tutorial corrections
Merged pull request #24 from gimler/master.

tutorial
first draft of cookbook article
some tweaks to class descriptions
fixed some typos
cleaning up some sentences. better flow
wrote a quick introduction