Bump version to 0.20

iOS: fix examples

    - fix EmbedReader initial iPad orientation
    - fix TabReader shouldn't show controls

Android: Add initial support for Android platform

iPhone: reduce controller present and dismiss latency

    - add simple shutter to mask video start

iPhone: fix overlay resizing bug

iPhone: release updates

iPhone: fix UITabViewController rotation interaction

iPhone: release updates

iPhone: fix ReaderSample project path to ZBarSDK

iPhone: release updates