Rename and export stringify

[charleso]

Apologies if there's a reason for not exporting this in the first place.

[garyb]

It's not exported directly because show is the same thing... show probably should be something else though, so that it fits the informal law of printing valid PS code, so 👍 I think.

[charleso]

Yeah I don't like Show, it can cause subtle bugs when types change. :)

[damncabbage]

In case it's useful: the opening post of purescript/purescript#1675 lays out the objection to enforcing the use of Show pretty well:

The more types that do have Show instances, the more dangerous show becomes; given that it works on almost anything, and that the return type is just String (rather than something that mentions the input type like pure, for example) it's very easy to call show on the wrong thing. It's almost like using a dynamic language!

[garyb]

Oops, sorry this was left to languish!