Animation detail

[txs]

Wonderful project. However, for vertical transitions, the fading and sliding animation can be done not from the 100% bottom. I tried some of the example app on expo eg. react native paper element. the transition is from 30% of the height, which makes the transition more fluid on slower android devices. Thanks

tested on android

[Traviskn]

I'm open to PR's to update transitions. An even nicer feature would be the ability to pass in a custom animation config, but that would be a lot more work.