Add {Input,Output}Stream support

[michaelbull]

This change adds support for InputStream and OutputStream options:

    private val input by option().inputStream().defaultStdin()
    private val output by option().outputStream().defaultStdout()

The option uses the FILE metavar and uses the Path completion candidates.

As is the common convention of many command-line tools, passing a hyphen (-) will serve as a substitute for stdin/stdout.

The sample demonstrates a reimplementation of the common md5sum utility:

$ echo 'hello world' > input.txt
$ cat input.txt | ./runsample stream
  md5sum: d41d8cd98f00b204e9800998ecf8427e

[ajalt]

Great idea!

[michaelbull]

Thanks @ajalt. When should we expect the next release? I'd like to start adopting this in my codebases.

[ajalt]

I don't have a release timeline, but you can use the snapshot build from sonatype or jitpack in the meantime. That would also be helpful so that you could test it out prior to release.