utils: new Memoize

* Removes unnecesary duplicated memoize.

* Adds InstanceMethodMemoize for memoizing instance methods.

* Renames Memoise to Memoize.

Signed-off-by: Mateusz Susik <mateuszsusik@gmail.com>
@MSusik be careful about changing existing API. I think in this case you shouldn't rename the argument.