Working small-to-normal support merging

Fixed fatal bug with anchors for mini supports

Make the optimization cleaner in support generatior

Much better widening behaviour

Add an optimizer interface and the NLopt implementation into libslic3r

New optimizer based only on nlopt C interfase
Fix build and tests

tests/sla_print/sla_print_tests.cpp

@@ -4,6 +4,8 @@
 
 #include "sla_test_utils.hpp"
 
+#include <libslic3r/SLA/SupportTreeMesher.hpp>
+
 namespace {
 
 const char *const BELOW_PAD_TEST_OBJECTS[] = {
@@ -228,3 +230,12 @@ TEST_CASE("Triangle mesh conversions should be correct", "[SLAConversions]")
         cntr.from_obj(infile);
     }
 }
+
+TEST_CASE("halfcone test", "[halfcone]") {
+    sla::DiffBridge br{Vec3d{1., 1., 1.}, Vec3d{10., 10., 10.}, 0.25, 0.5};
+
+    TriangleMesh m = sla::to_triangle_mesh(sla::get_mesh(br, 45));
+
+    m.require_shared_vertices();
+    m.WriteOBJFile("Halfcone.obj");
+}