reworking DCEL API, files clean-up (renamed walk_search.h into walk.h, removed tree_search.h, now replaced by r_tree.h)

Author: AlePalu

fdaPDE/geometry.h

@@ -35,8 +35,7 @@
 // algorithms
 #include "src/geometry/kd_tree.h"
 #include "src/geometry/r_tree.h"
-/* #include "src/geometry/tree_search.h" */
-#include "src/geometry/walk_search.h"
+#include "src/geometry/walk.h"
 // data structures
 #include "src/geometry/triangulation.h"
 //#include "src/geometry/interval.h"