Exclude parameters from memoize cache key

[sallyruthstruik]

There are several cases when you may want to exclude some parameters from cache key generation. For example:

@cache.memoize(timeout=1000)
def search(title, softIds):
    #some search stuff

search("Title 1", {1, 2, 3})
search("Title 1", {3, 2, 1})

in this case we want second search to be taken from cache, but it didn't. I propose this solution:

@cache.memoize(timeout=1000, exclude_params=["softIds"])
def search(title, softIds):
    #some search stuff

exclude_params - array of parameter names which should be excluded from key generation. So key will be based only on "title" parameter, and second search will be taken from cache.

[sallyruthstruik]

Added pull request #9