Add support for preferred scrolling direction.

• Support android:text even when character list is not set in XML
• Support wraparound animation for going forwards as well as backwards

Refer to https://github.com/robinhood/ticker/blob/master/2_0_migration.md

• Fix bug where ticker column size doesn't change after text size change.
• Fix debounce bug when setting the same text on ticker.
• Support tools:text.

• Add support for getText().
• Add support for android:text and app:ticker_defaultCharacterList.

• Add support for textStyle and text shadow attributes.
• Fix levenshtein bug that caused characters to disappear in animations.
• Update gradle dependencies

• Add minimum support for arbitrary characters.
• Update support and gradle dependencies.

• Performance optimizations for re-measure and re-layout.
• Better size change animation with Levenshtein algorithm.
• Added support for animateMeasurementChange to animate size changes smoothly during size change. This will call requestLayout() on every animation frame so use with care.
• Added support for animator listener to listen to updates by the main animator.

• BREAKING: changed app:ticker_textColor into android:textColor and app:ticker_textSize into android:textSize.
• Added support for getting/setting type face programmatically.
• Added support for app:ticker_animationDuration, android:gravity, android:textAppearance.