Moved some math macros (sqr, lerp, clamp) to libslic3r.h

Added UNUSED macro to libslic3r.h, used it to reduce some compile warnings.

Split the Int128 class from Clipper library to a separate file,
extended Int128 with intrinsic types wherever possible for performance,
added new geometric predicates.

Added a draft of new FillRectilinear3, which should reduce overfill near the perimeters in the future.

xs/src/libslic3r/libslic3r.h

@@ -88,6 +88,10 @@ inline std::string debug_out_path(const char *name, ...)
 	#define PRINTF_ZU "%zu"
 #endif
 
+#ifndef UNUSED
+#define UNUSED(x) (void)(x)
+#endif /* UNUSED */
+
 // Write slices as SVG images into out directory during the 2D processing of the slices.
 // #define SLIC3R_DEBUG_SLICE_PROCESSING
 
@@ -142,6 +146,25 @@ inline std::unique_ptr<T> make_unique(Args&&... args) {
     return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
 }
 
+template<typename T>
+static inline T sqr(T x)
+{
+    return x * x;
+}
+
+template <typename T>
+static inline T clamp(const T low, const T high, const T value)
+{
+    return std::max(low, std::min(high, value));
+}
+
+template <typename T>
+static inline T lerp(const T a, const T b, const T t)
+{
+    assert(t >= T(-EPSILON) && t <= T(1.+EPSILON));
+    return (1. - t) * a + t * b;
+}
+
 } // namespace Slic3r
 
 #endif