Add automatic cach invalidation upon exeding maximum cache age

[Olian04]

Ex:

@cache(5*60)
def foo(a):
    return a * a

This would invalidate the cache of function foo, 5 minutes after it being called the first time.

>>> foo(2) # will cache
4
>>> foo(2) # will use cache
4
>>> # wait for 5 min
>>> foo(2) # will cache again

[rouilj]

I think using cachetools.TTLCache as the cache backend should handle what you want.