Issue 31 — Part 1

Quite some changes, but I think this releases #52 #39 (at least when I'm done with this one here on #31) and #75 for others to work on.
Bunch of tests to be added for #52 #39 and #75 as well... 
Right, the remove is about getting rid of the possibly stale value in there. The write (not again, as this is a memoizer, it will only write if it didn't write before, so we're sure the data makes it to the underlying SoR.