Clean up release-process.md and make descriptors more consistent

This addresses some (but not all) of the issues in #4185. It cleans up a
few things in release-process.md (such as indents) and makes the
descriptors more consistent, in terms of style and also naming (both of
the descriptors and the intermediate inputs). This doesn't change any of
the actual build scripts, other than to change the file names -- I didn't
want to accidentally break anything, though it looks like there are a few
things that could be improved and made more consistent. The big change
that it would be nice if someone were to make is to switch the OS X
intermediates from tarballs to zips for more consistency. I didn't do
that, because I don't know the details of how tar and zip/unzip work on
the command line, especially when it comes to determinism.