Publish conda-forge packages on GitHub releases

For the most part Anaconda.org is incredibly reliable. However periodically issues occur perhaps due to service providers (e.g. Amazon), which are beyond our control. It would be nice in situations like this to have an alternative location to get packages from. One potentially nice solution would be to place the packages on the feedstocks' GitHub releases. We could also include an index for the organization that would allow this to behave like a simplified channel.

xref: https://github.com/conda-forge/conda-forge.github.io/issues/90#issuecomment-210119223

cc @wesm @danielfrg @jjhelmus