add ability to inspect cached_function for keymap and ignored;
extend cached_function to have method to generate a key per given args and kwds;
add a test of usage workflow, both for class methods and for functions


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/klepto@566 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/klepto