ABS tests

[odino]

We should start thinking of including tests of ABS scripts in our CI workflow. Right now only go tests are triggered -- which is fine, but might lead to funny issue since these tests are minimal. Having full blown scripts running will eventually be a bit more robust, and a good complement to our go tests.

We could store all script tests under /tests and loop through files that look like:

// expect: 23
a = 10
a *= 2
echo(a)

So that we can compare the output with the expected one.