Exporting types for dynamic styles

[kylerjensen]

This commit adds exports for 3 useful type declarations: DynamicViewStyle, DynamicTextStyle, and DynamicImageStyle. Exporting these types provides for better code completion when creating an instance of one of these styles. Example usage:

const stylesheet = new DynamicStyleSheet({
    myViewStyle: {
      backgroundColor: new DynamicValue('#FFFFFF', '#000000')
    } as DynamicViewStyle,
    myTextStyle: {
      // ...
    } as DynamicTextStyle,
    myImageStyle: {
      // ...
    } as DynamicImageStyle
});

[DimitarNestorov]

0.2.2 released