Turn off warning from integer cast.
Define test fixture for linear filtering.
Remove slow implementation of 1D filters.
Use vector instead of raw array.
Change name and signature of column based filter.
Add unit test for row-based filter
Add unit test for column-based filter.
Change signature of `apply_row_derivative`.
Fix the implementation of `apply_row_derivative`.
Add unit-test for `apply_row_derivative`.
Add unit test for `apply_column_derivative`.
Fix implementation of `apply_column_derivative`.
Add unit test for `apply_gaussian_filter`.
Fix the implementation of the Gaussian filter.
Add unit test for Sobel.
Fix Sobel filter.
Add unit test for Scharr.
Fix Scharr filter.
Add unit test for Prewitt.
Fix Prewitt filter.