This commit brings in the entire history of the Gash project. There
are a few conflicts, which are explained below.
* .dir-locals.el: Combine both files.
* .gitignore: Combine both files.
* COPYING: Use the Geesh version with HTTPS URLs.
* README: Use the Gash README.
* guix.scm: Use the Geesh package definition (the Gash one is
preserved in gash.guix.scm).