Added more complex high-level tests.

Those test a broad spectrum of features and implementation details and
can be considered more of integration tests than anything else.

I added two sets of tests here: One consisting of my own code golf
solutions from codegolf.stackexchange.com. Those should provide a good
stress test for the parser and corner cases of the langage. Secondly I
added snippets I wrote for rosettacode.org that each showcase how to
approach a particular problem or how to use a specific language
feature. Those can probably be more of a metric what parts are still
missing to make Pash more useful in the real world (at least when used
as a programming and scripting language).