Auto apply revision in PKGBUILD if available

[MajoranaOedipus]

There are many packages on Hackage have revisions.

It would be nice if arch-hs TARGET -o DIR could generates:

prepare () {
  cd $_hkgname-$pkgver
  curl https://hackage.haskell.org/package/$_hkgname-$pkgver/$_hkgname.cabal -o $_hkgname.cabal
}

whenever there are revisions available. The url above is typically the where the revision located (I am not sure if there are exceptions.)

Also it would be super cool if $pkgrel can be number'of'revision + 1

Thank you for your great repo! This helps me manage my Haskell packages a lot. It is just a little bit annoyed that I have to add that prepare () {...} constantly.