TODO when breaking compatibility

[f-f]

The goal of this issue is to list all the things that we might want to do the next time we are going to break compatibility (probably when 1.0 will happen). The reason for this is that bundling breaking changes is always a good thing to do, since people will have to make changes anyways, and it's best to just do it once than to repeatedly have to do it.

Up to date list of things we might want to do:

• rename packages.dhall to package-set.dhall: the name packages is confusing because we have to explain it contains the package-set update: the ship for this has probably sailed, as now spacchetti has merged into package-sets, so everything is just called packages, so let's keep it like that for consistency
• stop publishing under purescript-spago on NPM, and only publish under spago: the fact that we publish both might be confusing
• start failing when package-sets don't include the minimum compiler version update: this cannot be done by design, as package sets might come from a hash as well. All we can do then is to log a warning "spago assumes that you know what you're doing since we cannot parse the version from the package-set tag"