readme.md: added badge and link to Packagist

Conflicts:
	readme.md
opened 2.2
Revert "DI: 'inject' option is enabled by default (experimental)"

This reverts commit d5b8b05ffbd032c11205a76b047def0a1ae295ba.

Conflicts:
	src/DI/ServiceDefinition.php
added some deprecation warnings for 2.0.x users
more readable exception strings