Add Memoizing Decorator Support

[grantjenks]

As described in DiskCache Development it would be great to have an lru_cache-like decorator to cache function calls.

I contacted Yuval Greenfield, the author of filecache and he said the missing decorator feature was what blocked him from using the module. His decorator accepts one argument, seconds before expiry.

I prototyped something simple in Issue #8. It should be relatively easy to combine it with the source from Python 3's functools.lru_cache

[grantjenks]

Example: http://funcy.readthedocs.io/en/stable/calc.html#memoize

[grantjenks]

Needs "typed=False" parameter. See: https://bugs.python.org/issue13227

[tamirOK]

@grantjenks , does decorator have to store cached data on disk?

[grantjenks]

Yes, I would expect it to use core.Cache internally.

[grantjenks]

Deployed at 2.8.2

The new feature is at FanoutCache.memoize and DjangoCache.memoize