Add Box, Hermite, and Lagrange filters

[RunDevelopment]

As not promised, some more filters :)

This PR adds the box, Hermite, and Lagrange filters. Some notes:

• Box is a very simple filter, so there's not much to say.
• Hermite uses the same implementation as the other cubic filters, but with a different support window.
• I just copied Lagrange from ImageMagick. I checked and it produces the same results as ImageMagick.

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Related to #12.

[kornelski]

This is making hard to choose the right filter. Can you expand doc comments on each filter describing its unique advantages and disadvantages?

[RunDevelopment]

Since a lot of filters are variants of each other with very similar properties, I tried to explain the relation between filters. I hope that is good enough.

I also linked to the filter explanation article from the README, because I feel like this article explains it lot better than I ever could.

[kornelski]

Thank you