[kjofnjdw] Squircle go

We consider a spectrum of possible go 囲碁 board shapes.  On one extreme is the traditional grid bounded by a square.  Only 4 of the boundary points are corners (a point having only 2 neighbors).  On the other extreme is diamond go in which most of the boundary points are corners.  The different boundaries correspond to curves of the form

abs(x)^s + abs(y)^s < C^s

with s=infinity for traditional go and s=1 for diamond go.  The exponents in between those extremes, as well as 0 < s < 1, yield a variety of other curvy shapes with a different mix of edge (3 neighbors) versus corner points along the boundary.  s=2 yields go on the grid points inside a rasterized circle.

Permit coefficients on the terms, producing rectangles, ellipses, and superellipses.  Consider using a different exponent for each quadrant.  But these shapes are not as elegant.