Documentation tweaks

[paldepind]

This PR makes three small changes to the documentation:

• Changes an instance of "curried" that should be "uncurried"
• Removes an outdated reference to rows in the Effect type
• Changes some wordings slightly to avoid past tense sentences that IMHO feels a bit "historical". For instance "traditionally, it has been difficult [...]" and "there has been no way of giving such functions types". This module is many years old 😉

I hope you like these changes 😄

[hdgarrood]

This looks good to me, although I think the ‘it makes it possible...’ construction is a bit unclear, since the word ‘it’ is used to refer to two different things in quick succession, do you think you can find a way to reword that to get rid of one of them?

[paldepind]

Good point @hdgarrood. I've changed the first "it" to a "this". To me that seems to remove the awkwardness.

[garyb]

Thanks!