Only valid as a `type` for a `CommandLineTool` output with no
`outputBinding` set.

The following

```
outputs:
  an_output_name:
    type: stdout

stdout: a_stdout_file
```

is equivalent to

```
outputs:
  an_output_name:
    type: File
    streamable: true
    outputBinding:
      glob: a_stdout_file

stdout: a_stdout_file
```

If there is no `stdout` name provided, a random filename will be created.
For example, the following

```
outputs:
  an_output_name:
    type: stdout
```

is equivalent to

```
outputs:
  an_output_name:
    type: File
    streamable: true
    outputBinding:
      glob: random_stdout_filenameABCDEFG

stdout: random_stdout_filenameABCDEFG
```

If the `CommandLineTool` contains logically chained commands
(e.g. `echo a && echo b`) `stdout` must include the output of
every command.
