Moved legacy code into archive, ready for a new rapid(?) prototype.

I may regret doing this!

archive/c/memory/cursor.c

@@ -0,0 +1,9 @@
+/*
+ * a cursor is a cons-space object which holds:
+ * 1. a pointer to a vector (i.e. a vector-space object which holds an
+ *    array of `cons_pointer`);
+ * 2. an integer offset into that array.
+ *
+ * this provides a mechanism for iterating through vectors (actually, in
+ * either direction)
+ */