Create minimal test suite

[s1na]

Now that we have multiple implementations of scout, it'd be nice if they could test their compatibility with a test suite (like the ethereum state tests). As suggested by @axic this could be a set of yaml files which use the API in a predictable way.

The goals would be to ensure an implementation has a matching API and the host function semantics are correct (i.e. should test for edge cases, like overflow on bignum methods), and that the YAML file format conforms to spec.