$.Cache improvements

Cache::has(key) added
overflow eviction now happens at the time of the overflow (not the next read)
$.Cache.capacity is now 10000
replace some constant expressions with actual constants

avoids an extra level of recursion when hashing
memoize uses $.hash, and a Cache object (get,set,has)

this lets one use a new $.Cache() as a drop-in upgrade
move hash tests into their own file

added and fixed tests for hashing arguments objects
added tests for memoize
v0.2.16