Added test projects for libslic3r and fff_print.

Added test_geometry.cpp from upstream slic3r, thanks @lordofhyphens
Added circle_taubin_newton() for circle center calculation, thanks @lordofhyphens

tests/libslic3r/libslic3r_tests.cpp

@@ -0,0 +1,15 @@
+#define CATCH_CONFIG_MAIN
+#include <catch2/catch.hpp>
+
+#include "libslic3r/libslic3r.h"
+
+namespace {
+
+TEST_CASE("sort_remove_duplicates", "[utils]") {
+	std::vector<int> data_src = { 3, 0, 2, 1, 15, 3, 5, 6, 3, 1, 0 };
+	std::vector<int> data_dst = { 0, 1, 2, 3, 5, 6, 15 };
+	Slic3r::sort_remove_duplicates(data_src);
+    REQUIRE(data_src == data_dst);
+}
+
+}