Add more tests

[mell-o-tron]

We need a more comprehensive test suite, to more accurately check out what breaks and what does not whenever a change is made.

Tests are located in ./test/.

• There is a pass directory containing numbered .perk test files and their corresponding .expected file (containing the expected output of each test). These are the tests that should not fail.
• There is a fail folder with the tests that should fail. For these tests, no .expected file is needed.

The tests are run from the terminal with the following make targets:

• make test_pass to run tests for programs expected to pass;
• make test_fail to run tests for programs expected to fail;
• make test to run both test_pass and test_fail.

Additionally, you can pass a filename (or a filename prefix) after any of these targets to run a specific test.

Any PR providing at least five new tests will be accepted. In creating new tests, focus on weird edge cases or programs that should work but don't.