simplify api + improve minimum cell quality in 2d

[krober10nd]

141

• single step at the end to do laplacian smoothing...dramatically improves minimum element quality in 2d.
• must re-run benchmarks.

[krober10nd]

@jorgensd I also added a delete_low_quality_boundary_cell step at the very end before exiting generate_mesh.

The order of the delete boundary cells can be fiddled with. I suspect there's probably an optimal order but as it is in now, it's a significant improvement in minimum cell quality than what it was.

Here is the BP2004 benchmark ran again with the new changes

and here is the disk benchmark (a 40-50 % improvement in minimum cell qualities).

[krober10nd]

It will be interesting to see how this changes @nschloe benchmarks in meshgen_comparison.

[krober10nd]

okay, after rearranging the location of delete_boundary_entities around the laplacian smooth, min. qualities appear more stable.

for the BP2004 model.

[krober10nd]

143