adjoint filter cleanup and additions

[tylerflex]

• Adds a CircularFilter, which is just a uniform "cylinder" kernel instead of a conic kernel.
• Rename feature_size to radius in the circular filters.
• Remove extra factor of sqrt(3) in the radius calculation, which is inconsistent with literature.

Note: initial testing of the circular filter is showing that it's terrible compared to conic filter, so not mentioning it in the changelog for now.

[tylerflex]

Made edits based on Emerson's comments

1 - The descriptions for the Conic and Circular filters are the same.
2 - The title of vmax on line 134 should be "Max value".
3 - As the filter radius is general, maybe describe it using only "Radius of the circular filter to convolve with supplied spatial data." in line 27.

[momchil-flex]

Looks good, just some epxlanation about the difference between conical and circular filter somehwere?

[tylerflex]

Thanks, I added a bit more explanation and recommendation that the user use a conical mask (note each of them have the formula of the kernel already).