WIP: Separate GenericPackageDescription from PackageDescription

[Ericson2314]

Now, neither contains the other, and their common fields are contained in 'CommonPackageDependencies'.

I'll probably first merge a change adding lenses per components, so some stuff can be made {Generic,}PackageDescription-polymorphic in advance. (The lenses would of course preserve the cond tree structure.)

Please include the following checklist in your PR:

• Patches conform to the coding conventions.
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CC @kmicklas

[Ericson2314]

BTW, how do I get pems to cancel AppVeyor build?

[23Skidoo]

AppVeyor has underdeveloped account structure that doesn't map to GitHub orgs, but I remember that @hvr managed to do it by logging in to AppVeyor using my user name somehow.

[ulysses4ever]

@Ericson2314 any thoughts on this PR of yours? Do you still plan to work on it? If not, do you think it'd be worthwhile for someone else to finish it? Or maybe it's not relevant at all anymore, and we should just close?

[Ericson2314]

@ulysses4ever it has been a long time, but yes I think it might be worthwhile for someone else to complete this. Unless my memory is faulty or something changes over the past few years, our data structures currently do a very bad job of making illegal states unrepresentable.

[Mikolaj]

This is badly bit-rotted. Let me close, but mark as worth reviving (probably in a new PR, given the state of the patch?).

[Ericson2314]

Sounds good.