memoization functions

 This package provides memoization functions. `memoize' accepts a
 symbol or a function. When given a symbol, the symbol's function
 definition is memoized and installed overtop of the original function
 definition. When given a function, it returns a memoized version of
 that function.
 .
 Memoization takes up memory, which should be freed at some point.
 Because of this, all memoization has a timeout from when the last
 access was.