Accept multiple paths and distinguish between inner paths and the outer path.

- cameo/path.h, cameo/path.c (path_replace): replace a path in a list of
  paths with a different path
- cameo/path.h, cameo/path.c (path_find_leftmost): find the leftmost path
  in a list of paths
- cameo/path.h, cameo/path.c (path_free): move freeing of points to separate
  function free_points, for sharing with path_replace
- cameo/cameo.c (main): move path processing to new function process_paths
- cameo/cameo.c (process_paths): treat the leftmost path a outside path and
  process it last. Treat all others as inside paths.

cameo/path.c

@@ -20,6 +20,25 @@
 #include "path.h"
 
 
+static void free_points(struct point *points)
+{
+	struct point *next;
+
+	while (points) {
+		next = points->next;
+		free(points);
+		points = next;
+	}
+}
+
+
+void path_free(struct path *path)
+{
+	free_points(path->first);
+	free(path);
+}
+
+
 struct path *path_new(double r_tool)
 {
 	struct path *path;
@@ -77,6 +96,17 @@ void path_add(struct path *path, double x, double y, double z)
 }
 
 
+void path_replace(struct path *old, struct path *new)
+{
+	struct path *next = old->next;
+
+	free_points(old->first);
+	*old = *new;
+	old->next = next;
+	free(new);
+}
+
+
 struct path *path_reverse(const struct path *path)
 {
 	struct path *new;
@@ -265,14 +295,20 @@ struct path *path_offset(const struct path *path, int left, int notch)
 }
 
 
-void path_free(struct path *path)
+struct path *path_find_leftmost(struct path *path)
 {
-	struct point *next;
+	const struct point *p;
+	struct path *best = NULL;
+	double best_x = HUGE_VAL;
 
-	while (path->first) {
-		next = path->first->next;
-		free(path->first);
-		path->first = next;
+	while (path) {
+		for (p = path->first; p; p = p->next)
+			if (p->x < best_x) {
+				best = path;
+				best_x = p->x;
+				break;
+			}
+		path = path->next;
 	}
-	free(path);
+	return best;
 }