1.0.0-alpha.2

This is the second alpha version for 1.0.0 release. Mostly bug fixes.

• fix an issue where the duration is incorrect when resuming an animation with delay
• fix a performance issue with interactive transition
• remove most of the force unwrapped optional
• fix a crash where finish/cancel is called before the animation has started.
• make internal CAMediaTimingFunctions public
• default container color is now black. to customize, construct your own HeroTransition object.

Example project

• animate tabbar so that it doesnt cover the content
• add a playground in the example project for quick tests