Update schema to match API proposed in RFC

[jkutner]

The schema and routes exposed should be updated to match buildpacks/rfcs#125

[elbandito]

@jkutner I think some of the schemas are inconsistent on the RFC

These examples look correct to me:

https://registry.buildpacks.io/api/v1/search?matches=projectriff
https://registry.buildpacks.io/api/v1/buildpacks/projectriff/command-function
https://registry.buildpacks.io/api/v1/buildpacks/projectriff/command-function/1.4.1

But I think we must have been a type in the URL/links in the body. Looks like we're putting buildpacks before /api when it should come after v1/.

For example:

  "versions": {
    "1.4.1": {
      "link": "https://registry.buildpacks.io/buildpacks/api/v1/projectriff/command-function/1.4.1"
    },
    "1.3.9": {
      "link": "https://registry.buildpacks.io/buildpacks/api/v1/projectriff/command-function/1.3.9"
    }
  }

Should probably be:

  "versions": {
    "1.4.1": {
      "link": "https://registry.buildpacks.io/api/v1/buildpacks/projectriff/command-function/1.4.1"
    },
    "1.3.9": {
      "link": "https://registry.buildpacks.io/api/v1/buildpacks/projectriff/command-function/1.3.9"
    }
  }

Are there other things that are incorrect?