Add preferred package JSON format handler

[potomak]

Example response:

{
  "deprecated-version": ["0.1.0"],
  "unpreferred-version": ["0.2.0"],
  "normal-version": ["0.3.0", "0.3.1"]
}

[hvr]

This is almost what I need for hackage-cli (and other tooling I'm working on) to avoid scraping the package content HTML page... :)

...have you seen #338? I don't think we need to split up all information provided in /package/:package into several micro-endpoints. I'd rather expect an /package/:package.:format endpoint providing more information; For instance, I need to know for each single version what the highest x-revision is, as well when the tarball was uploaded, whether a documentation tarball is available. Splitting that information into several sub-endpoints would require a lot of HTTP GET traffic to reconstruct what /package/:package.html already provides now...

[hvr]

PS: I'm not saying that this endpoint shouldn't become JSON aware, since it's just an enhancement of an existing one...

[potomak]

@hvr I agree, and yes, maybe this could just be another format of the resource /package/:package/preferred waiting for an implementation of the handler that responds to /package/:package JSON requests.

[potomak]

What do you think about adding this handler to the preferred versions feature, to support the JSON format @gracenotes?

[dcoutts]

@potomak @hvr yes, providing a .json at the main package page is a good idea, but a bigger undertaking. I'm happy to merge this as is for now.

[potomak]

@dcoutts thanks. How can I get notified about the deployment of this feature?

[dcoutts]

@potomak missed the deployment window yesterday, but aiming to do it this evening instead.