message: Add velocity
diff: @@ -2,7 +2,7 @@ import React from 'react'
  const withGesture = Wrapped =>
  class extends React.Component {
  - state = { x: 0, y: 0, xDelta: 0, yDelta: 0, xInitial: 0, yInitial: 0, down: false }
  + state = { x: 0, y: 0, xDelta: 0, yDelta: 0, xInitial: 0, yInitial: 0, xPrev: 0, yPrev: 0, down: false }
  handleTouchStart = e => this.handleMouseDown(e.touches[0])
  handleTouchMove = e => this.handleMouseMove(e.touches[0])
  @@ -21,7 +21,7 @@ const withGesture = Wrapped =>
  window.addEventListener('touchend', this.handleMouseUp)
  window.addEventListener('mousemove', this.handleMouseMoveRaf)
  window.addEventListener('mouseup', this.handleMouseUp)
  - const newProps = { ...this.state, x: pageX, y: pageX, xDelta: 0, yDelta: 0, xInitial: pageX, yInitial: pageY, down: true }
  + const newProps = { ...this.state, x: pageX, y: pageX, xDelta: 0, yDelta: 0, xInitial: pageX, yInitial: pageY, xPrev: pageX, yPrev: pageY, down: true }
  this.setState(this.props.onDown ? this.props.onDown(newProps) : newProps)
  }
  @@ -30,7 +30,7 @@ const withGesture = Wrapped =>
  this._busy = true
  }
  handleMouseMove = ({ pageX, pageY }) => {
  - const newProps = { ...this.state, x: pageX, y: pageX, xDelta: pageX - this.state.xInitial, yDelta: pageY - this.state.yInitial }
  + const newProps = { ...this.state, x: pageX, y: pageX, xDelta: pageX - this.state.xInitial, yDelta: pageY - this.state.yInitial, xPrev: this.state.x, yPrev: this.state.y, xVelocity: pageX - this.state.x, yVelocity: pageY - this.state.y }
  this.setState(this.props.onMove ? this.props.onMove(newProps) : newProps, () => (this._busy = false))
  }
  