Implement quality improvement

[jdugge]

Implement the quality improvement algorithm described in Shewchuk's Delaunay Refinement Algorithms for Triangular Mesh Generation

• for each boundary edge (or, more generally, each input edge), check if it is encroached by a vertex (i.e. has a vertex inside its diametral circle)
  • if it does, split the edge in half
• for each triangle, check if it it is skinny (i.e. has a circumradius-to-shortest-edge ratio greater than B)
  • if it is, insert the off-center as a new vertex

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• [x] Scan boundary edges
• [x] Check encroachment
• [x] Split edge
• [x] Calculate circumradius-to-shortest-edge ratio
• [x] Find off-center
• [x] Insert off-center

[jdugge]

This completes the ingredients for the Ruppert/Shewchuk/Üngör algorithm.