eulerr 3.0.0

Major changes

• Ellipses are now supported by setting the new argument shape = "ellipse" in euler(). This functionality accompanies an overhaul of the innards of the function.
• Initial optimization function and gradient have been ported to C++.
• The initial optimizer has been switched from stats::optim(..., method = "L-BFGS-B") to stats::nlminb().
• The final optimizer now falls back to GenSA::GenSA() when the fit from nlminb() isn't good enough, by default for 3 sets and ellipses, but this behavior can be controlled via a new argument control.
• A packing algorithm has been introduced to arrange disjoint clusters of ellipses/circles.
• The label placement algorithm has been rewritten to handle ellipses and been ported to C++. It now uses numerical optimization, which should provide slightly more accurate locations.
• The initial optimizer now uses an analytical Hessian in addition to gradient.

Minor changes

• The initial optimizer now restarts up to 10 times and picks the best fit (unless it is perfect somewhere along the way).
• The default palette has been changed to a fixed palette, still adapted to color deficiency, but with some manual adjustments to, among other things, avoid unnecessary use of color.
• The names of the diagError and regionError metrics have been changed from diag_error and region_error to reflect the original names.
• The coordinates for the centers are now called h and k instead of x and y, respectively.
• A new label() function has been added to extract locations for the overlaps for third party plotting (#10).
• The counts argument to plot.euler() and panel.euler.labels() have been deprecated in favor of the more appropriate quantities.
• Argument fill_opacity in plot.euler() that was deprecated in v2.0.0 has been made defunct.