No compile only implementation

No compile only implementation, also textZoom as xml property

MathView now follows Observer pattern

MathView now implements Observer pattern!

Stable pre-release, works with DataBinding Library

The mistakes in implementation sovled, now MathView works with Android DataBinding library.

Kotlin style update

• Getters and Setters in more Korlin style
• Reference text in xml (will be tested with databinding)
• Not calling update() automatically to render MathView less times

Stable pre-release

Stable pre-release version with small interface