This release addresses the issue of arbitrary big key lengths. From this point forward, keys will be hashed by default in the form described at the end of changelog.
Changelog:
* Create `utils.hash_key` function.
* Add `_hash_key` keyword argument to `cached` function. (resolves 7)
+ `_hash_key` defaults to `True`.
+ If `_hash_key` is set to `True`, keys generated from function calls are hashed and returned with fixed size of 65: first 32 symbols are md5 cache of [function qualified name](https://www.python.org/dev/peps/pep-3155/), symbol 33 is '_', and last 32 symbols are md5 cache of function arguments.