v5.0.0-beta1

Version 5.0.0-beta1

 - `isOpen` is now a property #899
 - Allow reopening after an open error #910
 - Change parsers to be transform streams #922
 - port.path is now read only #898
 - Remove lowercased options #898
 - Switch to Lie as a promise library (smaller)
 - [unix] Flush now gives errors and flushes tx and rx #900