Fix Berghaus clip region.
Fix Berghaus clip region.

The tips of the lobes were coincident at [180°, 0°], which caused issues
with D3’s clipping.  Instead, we generate a circle around [180°, 0°]
with an appropriate number of points, and use these as the lobe tips.

Fixes #3.

cbtpro/d3-geo-projection,Fil/d3-geo-projection,paulkogel/d3-geo-projection,GerHobbelt/d3-geo-projection,emilbayes/d3-geo-projection,jswiss/d3-geo-projection,Fil/d3-geo-projection