Improve test scripts:

  tools/test-server

    This is a server to run on an ARM machine. It will listen to
    POST requests on port 8080 containing ARM assembly code and
    return a JSON response with the output after linking with
    libminijava and running the executable. Or an error if linking
    failed or the executable left a non-zero exit status.

  tools/test-client.py

    Is a client which can be used to either run a .java file with
    Java, or compile it with mjc and send it to the test server,
    or do both and then compare the result.