Prember / Multiple File Support

[Prember](https://github.com/ef4/prember) pre-renders routes into a static directory structure with index.html files at build time. I'd like to be able to use the lightning strategy for deployment and pre-render my static routes. This can be supported by grabbing the files from s3 as assets, but you lose the ability to effectively use revisions, uploading the html as assets using the s3 plugin means the index.html files will be overwritten as they are not fingerprinted. I would like to upload all the html into redis just as it stores the main ember index.html file to retain the ability to have revisions.

I've noticed in the [past a PR](https://github.com/ember-cli-deploy/ember-cli-deploy-redis/pull/80) was rejected, as a use case didn't really exist at the time and the suggestion of using the plugin multiple times as part of the pipeline was the correct advice. The past issues and pr were about uploading a single other file. An app may have tens or hundreds of static routes being prerended by prember so creating a plugin entry for each html file would be cumbersome, prone to error and not very scalable.

I'm creating this issue to spark at the least a discussion about if prembers rising popularity changes the conversation around supporting multiple file support and if it should be pursued as part of this plugin.

Start by reviewing the plugin's existing index.html upload entry point and the rejected ember-cli-deploy-redis PR #80, then compare the multiple prerendered HTML files produced by Prember with the current pipeline advice. Done means the project has an agreed, implementable approach for storing multiple HTML files without collisions while preserving revisions.

Written by the indexing model from the issue text.