Add module to precompute the sequence of tiles to draw circles

This is a work in progress. I have implemented two steps of my
algorithm so far:

  A) compute the maximum width expected based on the total number
     of authors, adding an error margin to account for circles
     larger than expected

  B) compute distance values up to a threshold for all tiles within
     a sector of circle between the vertical axis x=0 and the
     diagonal axis x=y

I have also implemented the power2() utility function to compute
and cache the squares of numbers. The same values are used frequently
in the computation of distances within the circle sector.