Redirection verifier needs to handle multiple redirection files

[Genevieve Warren]

1. Needs to account for possibility of multiple redirection files. All redirection files (if there is more than one) will be listed in the .openpublishing.publish.config.json file like so:

"docsets_to_publish": [
    {
      ...
      "build_entry_point": "docs",
      "redirection_files": [
        ".openpublishing.redirection.json",
        ".openpublishing.redirection.architecture.json",
        ".openpublishing.redirection.azure.json",
        ".openpublishing.redirection.core.json"
      ],
      ...
    }

2. For redirects that use source_path (as opposed to source_path_from_root), the path to the file is relative to the location of the redirection file that contains it. So we need to check the path a little differently for this one.

[Genevieve Warren]

I'm currently working on no. 1.