message: add m + p utilities to Button
diff: import React from 'react'
  import classnames from 'classnames'
  import PropTypes from 'prop-types'
  +import {mapWhitespaceProps} from './props'
  -function Button({tag: Tag = 'button', children, size, block, linkStyle, grouped, scheme, onClick, disabled, ...props}) {
  +function Button(props) {
  + const {
  + tag: Tag = 'button',
  + children,
  + size,
  + block,
  + className,
  + linkStyle,
  + grouped,
  + scheme,
  + onClick,
  + disabled,
  + ...rest
  + } = mapWhitespaceProps(props)
  const classes = classnames(
  + className,
  {
  btn: !linkStyle,
  'btn-link': linkStyle,
  @@ -16,7 +31,7 @@ function Button({tag: Tag = 'button', children, size, block, linkStyle, grouped,
  )
  return (
  - <Tag {...props} type="button" disabled={disabled} onClick={disabled ? undefined : onClick} className={classes}>
  + <Tag {...rest} type="button" disabled={disabled} onClick={disabled ? undefined : onClick} className={classes}>
  {children}
  </Tag>
  )
  