Add "common" config for multiple users on same machine

[todbot]

A user wrote in wanting to use a common config file across multiple users on a Windows machine. Some questions:

• Can we use symlinks or hardlinks on Windows to do this?
• How to specify the location of the config file?
• Perhaps common config file is a list of overrides for per-user config file
• Or it specifies "master" values that cannot be changed per-user