Change minSdkVersion from 23 to 21

0.3

Lower minSdkVersion from 23 to 21

RecyclerItem extra validation + minor refactoring

• RecyclerItem: added extra logic for detecting cases when RecyclerItem.variableId cannot be found in the given RecyclerItem.layoutId. An IllegalStateException with a detailed message will be thrown in this case.
• Minor refactoring.

Initial release

v0.1

Initial commit