Implement new EIP-1193 API

Added

• The most recent EIP 1193 API (#30)
  • The method request
  • The events disconnect and message
• A global initialization event, ethereum#initialized, for
  asynchronous injection (#31)
• Helper methods for initializing the provider (#31)

Changed

• BREAKING: Use named instead of default exports (#31)
• BREAKING: MetaMaskInpage constructor now takes a connectionStream and an
  options object (#31)
• BREAKING: _metamask.sendBatch -> _metamask.requestBatch (#30)
• BREAKING: Revert send to match provider in v7.7.8 of metamask-extension (#29)
• The connect event now emits with a ProviderConnectInfo object per EIP 1193 (#30)
• Deprecated the send method (#30)
• Deprecated the events close, networkChanged, and notification, and
  added deprecation warnings for them (#30)
• Un-deprecated sendAsync (#29)