This adds the ability for per-account signatures in the accounts.conf
config file. The signature is added to emails in the editor at the
bottom of the email. This includes when forwarding, replying to, and
composing emails.
There are two config options: signature-file and signature-cmd. The
former allows a signature to be read from a file and the latter allows
an arbitrary command to be executed to return the signature.
The config options have been documented in aerc-config
The unsubscribe command, available when in a message viewer context,
enables users to easily unsubscribe from mailing lists.
When the command is executed, aerc looks for a List-Unsubscribe header
as defined in RFC 2369. If found, aerc will attempt to present the user
with a suitable interface for completing the request. Currently, mailto
and http(s) URLs are supported. In the case of a HTTP(S) URL, aerc will
open the link in a browser. For mailto links, a new composer tab will be
opened with a message filled out according to the URL. The message is
not sent automatically in order to provide the user a chance to review
it first.
Closes#101
