Fix Constructor Not Found and Proguard Rules Addition

Features

1. This release fixes the constructor not found exception when minify is enabled.
2. The proguard rules are added to keep the classes annotated with @Layout along with the generated classes required by the library

Note:

A new annotation @Keep is added for the purpose of keeping the class and its methods when minify is enabled. This was required by the library so to reference the generated classes for the item views.
This annotations as a by product can be utilised by the client code to prevent any class from being obfuscated.