add struct ct_surface as a struct _win_st (ncurses) replacement

src/surface.h

@@ -0,0 +1,16 @@
+#ifndef _CURSETREE_SURFACE_H
+#define _CURSETREE_SURFACE_H
+
+/* Initial row and column coordinates */
+#define ROW0 1
+#define COL0 1
+
+typedef unsigned short pos;
+
+typedef struct ct_surface {
+  pos x, y, w, h;
+  char **buf;
+  pos vcx, vcy; /* virtual cursor position */
+} surface;
+
+#endif /* _CURSETREE_SURFACE_H */