Mag - processing - reduction to Pole

[lheagy]

In the lecture, there is discussion on reduction to pole for mag data, however we do not have anything on it in the GPG. Perhaps we should include a brief discussion (even just at the conceptual level) in Mag Processing?

Also, in the discussion of half-width (#43), it would be beneficial to be able to reference this.

cc @dougoldenburg , @fourndo

[fourndo]

I should add it to the list of Filters indeed.
I can work on it later today.

[dccowan]

I added something on a separate branch. Haven't merged it yet though.

[dccowan]

Added a reduction to pole section. We can always change it if people have suggestions.