Improve output files

[niknetniko]

Again, split into files themselves and the "text" based output channels.

files

In TESTed, you were only able to provide a single output file using file. This has been extended to support multiple.

An output_file contains both a path and a content field, both of which are required.

• The path field specifies the path to the file that the student should have generated (in the working directory).
• The content field contains either the expected contents of the generated file or a path to a real file containing the expected contents (located in the evaluation folder).

tabs:
- tab: output_file
  contexts:
  - testcases:
    - expression: genereer('origineel_tekst.txt', 'text', 3)
      return: true
      output_files:
        - content: !path "files_tests/tekst1.txt"
          path: "text1.txt"
        - content: !path "files_tests/tekst2.txt"
          path: "text2.txt"
        - content: "Created using write mode.\n3\n"
          path: "text3.txt"
      input_files:
        - path: "origineel_tekst.txt"
          content: "Created using write mode.\n"

At the moment, these are all shown inline on Dodona.

See also #482

stdout and stderr

The same support is also added here, except path is not supported. (here this is basically a rename of data to content)

- tab: stdout
  contexts:
  - testcases:
      - stdin: "hello"
        stdout: 
          content: "hello world!\n"

In the future, we might also support path to generate things like submisson > stdout.txt if we have some use for that, but at the moment this is not supported.