Implement stack growth. In project 2, the stack was a single page at
the top of the user virtual address space, and programs were limited to
that much stack. Now, if the stack grows past its current size,
-allocate additional page as necessary.
+allocate additional pages as necessary.
Allocate additional pages only if they ``appear'' to be stack accesses.
Devise a heuristic that attempts to distinguish stack accesses from