Update StdOutputStream to keep trailing empty lines

[Michael1993]

Closes #750

Proposed commit message:

${action} (${issues} / ${pull-request}) [max 70 characters]

${body} [max 70 characters per line]

${references}: ${issues}
PR: ${pull-request}

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[Bukama]

Put a nice commit message on it and you are ready to merge :)

[nipafx]

After a lot of qualms, I settled on the basic assumption that every line, whether printed to System.out or read from System.in, ends with a newline (except with System.out.print). That leads to:

• print("Foo") ~> ...
  • capturedString: "Foo"
  • capturedLines: [ "Foo" ]
• println("Foo") ~> ...
  • capturedString: "Foo%n"
  • capturedLines: [ "Foo" ]
• println("Foo"), println() ~> ...
  • capturedString: "Foo%n%n"
  • capturedLines: [ "Foo", "" ]
• readln: "Foo" ~> ...
  • capturedString: "Foo%n"
  • capturedLines: [ "Foo" ]
• readln: "Foo", "" ~> ...
  • capturedString: "Foo%n%n"
  • capturedLines: [ "Foo", "" ]

The new behavior still needs to be documented. And the issue needs to prominently explain that the behavior changed and what the fix is. We can later copy-paste that to the release notes.

[nipafx]

I described the behavior in the feature doc. Can you take a look @Michael1993?

Once we agree on the phrasing and details in the there, we can expand it to the Javadoc (or at least add a reference there) and issue, so we have something to copy to the release notes.

[Michael1993]

The documentation looks fine to me.