Add initial tests

Add initial tests

The tests are meant to be run by pytest (just run `pytest` in the root
or `tests` directory once Normand is installed).

Each `.nt` file is a test, its prefix indicating the expectation:

`pass-`:
    Everything above the `---` line is the valid Normand input
    to test.

    Everything below the `---` line is the expected data
    (whitespace-separated hexadecimal bytes).

`fail-`:
    Everything above the `---` line is the invalid Normand input
    to test.

    Everything below the `---` line is the expected error message
    having this form:

        LINE:COL - MESSAGE

Change-Id: I65c0276f418c252735f75e583023772194b9eb4a
Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>