Issue #4: Change BEAN_METHOD_NOT_IN_CONFIGURATION from error -> warning
Since Spring does explicitly allow @Bean methods in non-configuration
classes (so-called 'lite mode'), the annotation processor should only
issue a warning and not an error.

See
http://docs.spring.io/spring/docs/3.2.x/javadoc-api/org/springframework/context/annotation/Bean.html
Merge pull request #5 from ferstl/bean-within-configuration-adjustment

Issue #4: Change BEAN_METHOD_NOT_IN_CONFIGURATION from error -> warning