v1.2.1 - Zoomish

This release wants to improve cluster's press-to-zoom default behavior, while allowing more expert developers to access underlying clustering engine and completely override default press-to-zoom feature.

This has been done by:

• using react-native-maps fitToCoordinates (and edgePadding) for greater accuracy and control over press-to-zoom
• introducing new prop for controlling whether default press-to-zoom should be preserved even if onClusterPress is passed as prop
• passing clustered markers data as parameter of onClusterPress, in order to allow complete control over the cluster's child markers
• exposing clustering engine instance