Reinstate and rename test file for Gaussian pyramid.
Rename files again.
Change header inclusion style.
Fix laplacian function.
Fix compilation errors in `Warp.hpp`.
Change typedef name.
Cast channel value instead of conversion.
Fix guards.
Fix called method name.
Use `PixelTraits::zero` instead of `0`.
Add stub tests for Gaussian pyramid.
Fix copy constructor of the `Pixel` class.
Merge pull request #145 from DO-CV/maint-test-dog-pyramid

[MAINT] Add unit tests for Gaussian pyramid.