Fix up packaging and directory organization

Fixed these things that have been bugging me for a while:
- Rather than putting tests in namespaces called hesokuri.test-hesokuri.foo, but
  them in hesokuri.foo-test. The latter is shorter, flows better, makes the test
  namespaces easier to distinguish from the actual app namespaces (since they
  end with -test), and is apparently how Leiningen sets up the test directory as
  of the latest version.
- Move the "testing" shared testing code from src/hesokuri to test/hesokuri,
  which is more intuitive and consistent.