cameo: adding support for dril/mill substitutions (in progress)

- Makefile (OBJS): added shape.o
- README: added section for drill/mill substitutions
- lang.l, lang.y: added commands "drill", "empty", "mill", "remainder", and
  "reset"
- lang.y (clear_paths): moved freeing of all paths from "clean" to shared
  function clear_paths
- ops.h, ops.c (try_drill, try_mill): helper functions for "drill" and
  "mill" commands
- shape.h. shape.c (slot, circle): functions to generate toolpaths for
  basic shapes

cameo/ops.c

@@ -11,7 +11,10 @@
  */
 
 
+#include <stddef.h>
+
 #include "path.h"
+#include "shape.h"
 #include "ops.h"
 
 
@@ -54,3 +57,34 @@ void tool_comp_paths(struct path *paths, int dog_bone, int all_inside)
 				tool_comp_1(path, 0, dog_bone);
 	tool_comp_1(leftmost, !all_inside, dog_bone);
 }
+
+
+struct path *try_drill(struct path *path, double d_min, double d_max)
+{
+	struct path *new;
+
+	if (path->r_tool*2 < d_min || path->r_tool*2 > d_max)
+		return NULL;
+	if (!path->first || path->first != path->last)
+		return NULL;
+	new = path_new((d_min+d_max)/2); /* @@@ fishy */
+	path_add(new, path->first->x, path->first->y, path->first->z);
+	return new;
+}
+
+
+struct path *try_mill(struct path *path, double diam, double step)
+{
+	if (path->r_tool*2 < diam)
+		return NULL;
+	if (!path->first)
+		return NULL;
+	if (path->first == path->last)
+		return circle(path->first->x, path->first->y, path->first->z,
+		    path->r_tool, diam/2, step);
+	if (path->first->next == path->last)
+		return slot(path->first->x, path->first->y,
+		    path->first->next->x, path->first->next->y,
+		    path->first->z, path->r_tool, diam/2, step);
+	return NULL;
+}