FIX Shows initial collapse animation when using keepCollapsedContent #65, fixes "Instantly collapses on first collapse #55"

FIX: ReactMotion around static render #67, fixes React reconciliation so content is re-used properly

• Expose react-motions's onRest callback #56, props to @glauberramos

• Perf improvement: #52 Reduce Spring precision to 0.5 (from default 0.01)

• FIX Avoid setting height to 0 so we don't miss toggling open #50 by @jdeal

• FIX: Overflow hidden, when isOpened=true #39 by @Frumcheg

• FIX: When collapse is opened by default animation starts from 0 if content is changed #36, props - to @GeraldIstar

• Add: expose onHeightReady callback #43. Thanks, @nutgaard

Add React@15 support

#33 - changes for react-motion@^0.4 upgrade

New major release since breaking change for springConfig format
No other breaking changes though, so upgrade should be easy