4.1.0

• Update to Swift 4.1.
• Add AsyncCommand.stop, interrupt, suspend and resume. Also for Linux (#59, #60).
• Add runAsyncAndPrint command (#61).
• Improve documentation and formatting.
  Use present tense in documentation.
  Add missing documentation.

Bug fixes

• Make main.stdout.encoding default to main.encoding.
• run: do not read both standard output and standard error if they are the same.

Miscellaneous

• Mark stream's readData() with @discardableResult
• Make testIntsLazySplit_NoEmptySlices actually do something.
• Xcode 9.3: update to recommended project settings.
• Readme: update with new functionality.
  Also fix some other stuff.