Our repa pricer gives the same price as the original version using
explicit Euler.
Start moving the blog article towards using a plain repa array. Now
that we have lost the comonad there is no point in using a pointed
array.
Integrate the working code from Question.hs so we can do a spot ladder
and publish at least a part I of a blog. Pricing an Asian will take
some further work and although it's not much, I think it better to
publish what we have so far.