New functions for variable offsets of polygons / expolygons.

Test cases for the above.
Improvements of older test cases.

tests/libslic3r/CMakeLists.txt

@@ -2,7 +2,9 @@ get_filename_component(_TEST_NAME ${CMAKE_CURRENT_LIST_DIR} NAME)
 add_executable(${_TEST_NAME}_tests 
 	${_TEST_NAME}_tests.cpp
 	test_3mf.cpp
+	test_clipper_offset.cpp
 	test_config.cpp
+#	test_elephant_foot_compensation.cpp
 	test_geometry.cpp
 	test_polygon.cpp
 	test_stl.cpp