Preloaded hooks extend base hooks. They behave like the pytest fixture
with the `autouse` parameter. This is useful when writing a module and
using it with "auto" before/after hooks.

The following functions have been "preloaded" into `hooks.lua` module:
  - before_suite_preloaded(func)
  - after_suite_preloaded(func)
  - before_all_preloaded(func)
  - after_all_preloaded(func)
  - before_each_preloaded(func)
  - after_each_preloaded(func)

Close tarantool#380

The original `treegen` module (path: tarantool/test/treegen.lua) has
been moved to the current project with the following changes:
    - refactoring;
    - updated documentation.

Closes tarantool#364