Container aware migrations

Added section for container aware migrations
Merge pull request #50 from peterrehm/patch-1

Container aware migrations
Update composer.json
Merge pull request #52 from totaltrash/master

Updated composer.json for Symfony 2.3
Added explanation for manual tables

Added the description for schema_filter to allow manual tables.

doctrine/migrations#101
Fixed typo
Added configuration-block and fixed indenting
Replaced underscore with dash
Merge pull request #56 from peterrehm/patch-2

Added explanation for manual tables
Fixed the markup in the doc
corrected grammar
Merge pull request #59 from shieldo/patch-1

corrected grammar
Added missing line breaks for proper code rendering
Merge pull request #60 from peterrehm/patch-2

Added missing line breaks for proper code rendering
Issue #38 Multiple entity managers support

Added the possibility to configure migrations depending on
the entity manager