Possibility to declare @Result and @ConstructorArgs in POJO models instead of mappers. Supports extending POJO classes and declaring mappings both on constructors and fields.

Relates to #157 and #1612

Comment From: h3adache

I really like this feature. Thanks for doing the PR @alex-pozdnyakov!

Comment From: h3adache

@alex-pozdnyakov sorry for the late response on this. Can you resolve this merge conflict?

Comment From: pengcheng

This cl looks great, why not resolve the conflicts and merge the PR?

Thanks!