The "f" library is a rather thin translation layer for already
existing Emacs functions.  Most functions directly map to an already
existing function (eg. "f-no-ext" and "file-name-sans-extension").  For
this reason, removing "f" comes at no cost while reducing the number
of dependencies one has to count on and the user has to install.

Co-authored-by: Tino Calancha <tino.calancha@gmail.com>

Allow users to retrieve any secret field stored in the files.
Use auth-source-pass to retrieve the secret fields.
Bump version to v2.1.0.

* contrib/emacs/Cask: Replace dependency on `s' library
with auth-source-pass dependency.

* contrib/emacs/password-store.el
(password-store-url-field): New option.
(password-store-dir): Use `auth-source-pass-filename'.
(password-store-read-field, password-store-get-field)
(password-store-copy-field, password-store-parse-entry): New functions.
(password-store-read-field): Use password-store-parse-entry.
(password-store--save-field-in-kill-ring): New function extracted from
`password-store-get'.
(password-store-url): Use `password-store-get-field' and
`password-store-url-field'.

* contrib/emacs/README.md: Update documentation.

* contrib/emacs/CHANGELOG.md: Announce changes.

Instead of editing the password file directly using Emacs, "pass edit" is
run. This allows password-store's git change tracking to work.

This adds a dependency on the with-editor Emacs package.