Allow repodata.json and packages to live in separate locations by adding base_url property

Here’s a draft of a simple idea that IMO fills a need. Add a base_url so that repodata.json and packages can live in separate directories, without having to set up a redirecting proxy. base_url CEP by dholth · Pull Request #61 · conda-incubator/ceps · GitHub

One simple use case might be to use yesterday’s repodata.json. Download it somewhere ahead of time, set base_url, and point conda at the older repodata.json. Then you can see what conda would have done before the latest packages, patches etc.

Updated with a couple of use cases, behavior when base_url is not present, and repodata_version: 2 only when base_url is present.