[ELPA] New package: transient

[Jonas Bernoulli]

Hello,

I would like to add Transient [1] to GNU Elpa.  It comes with an Info
manual, which you can also read online [2].

  1: https://github.com/magit/transient
  2: https://magit.vc/manual/transient

The TL;DR is:

> Taking inspiration from prefix keys and prefix arguments, Transient
> implements a similar abstraction involving a prefix command, infix
> arguments and suffix commands. [...] When the user calls a transient
> prefix command, then a transient (temporary) keymap is activated,
> which binds the transient's infix and suffix commands, [...] The
> available suffix and infix commands and their state are shown in a
> popup buffer until the transient is exited by invoking a suffix
> command.

I admit that that is a bit technical and the manual even more so.
That obviously needs some work.  But that doesn't keep end-users from
successfully using these transient commands; Magit users already do.

Already a few third-party packages also use Transient.  It supersedes
Magit-Popup, which Magit previously used and which also has some third-
party users.  Hydra is another package that is somewhat similar.  The
manual comes with some comparisons [3].

  3: https://magit.vc/manual/transient/Related-Abstractions-and-Packages.html

Yes, this is actually a step towards adding Magit to GNU Elpa, which
some of you have asked for before, once or twice.  ;D

I have already signed copyright assignment for "Emacs".  Almost a week
ago I contacted address@hidden because my new employer also needs to
sign some things.  I re-send that message today.

  Cheers,
  Jonas