Release 1.16.0 – Update approach to `.gitignore`

This release changes the default .gitignore contents and the recommended practices around it.

The new approach is to add only project-specific rules in the .gitignore. Rules that apply to a person's way of doing things (and the particular tools they happen to use) should instead go into a user's global git ignore file. For example, Emacs checkpoint and backup files are things that are not specific to a given project; rather, Emacs users will see them created everywhere, in all projects, because they're a byproduct of using Emacs, not a consequence of working on a particular project. Thus, they belong in a user's global ignores list, not in this project .gitignore.