[updated] v4.0.0: Support Androidx Biometrics API

[Updated to support bugfixes]
Released on NPM

Supports Androidx 'Biometrics' API: https://developer.android.com/reference/androidx/biometric/BiometricPrompt

• enables Face Unlock on supported devices
• provides native prompt to authenticate
• retains backward compatibility with Samsung/MeiZu native drivers for Android <23
• brings Android to parity with iOS

Details:

• isSensorAvailable uses android BiometricManager
• provides 'Biometrics' biometryType, as opposed to 'Fingerprint'
• on Android Q (v29)+, uses device's preferred biometry type (user-decided)
• on Android P (v28) and below, defaults to Fingerprint, supported by FingerprintCompat lib
• on Android M-P (v23), checks for native fingerprint support on device (Samsung & MeiZu), and defaults to it if available
• updates README and examples doc to reflect