This is to add an Emacs companion of "guix build --file" and "guix package --install-from-file".
Patches: [PATCH 1/2] emacs: main: Remove top-level package tables. This patch finally rewrites that part of code in a functional style. Many thanks to Ludovic for past comments on using 'delay' and vhashes. [PATCH 2/2] emacs: Add 'guix-package-from-file' command. And this patch partially breaks the functional style. A new package (from an arbitrary file) must be registered in a table of packages, so that it can be addressed later (for example, if a user would want to install it). So this is done using not very functional 'set!' in 'register-package' procedure (at least it sets a local variable). Is there a better way to write this?
