Reformat code a little bit.
Clean header inclusion.
Add stub tests for the `ImagePyramid` class.
Rename variables and methods.
Remove redundant tests.
Add unit tests for `ImagePyramid` and `ImagePyramidParams`.
Eliminate unused variable warning.
Fixed wrong header inclusion.
Merge pull request #133 from DO-CV/maint-add-tests-for-image-pyramid

[MAINT] Add tests for the `ImagePyramid` class.