Intiial work for problem test framework. Works with lots of limitations.
git: ignore idea project files.
test: Support Erlang and simplified input format.
test: support C.

Also add staircases solution in C.
test: Simplify test code

Test helper methods (`on`, matchers) should be smart on their
parameters to make test cases code as simple as possible.
problem: inversions in array
test: more short test cases + "any" matcher.
problem: stacking boxes