[ELPA] New package: gcmh-mode

[Andrea Corallo]

Hi all,

I'd like to propose GCMH as GNU Elpa package.

It enforces a sneaky Garbage Collection strategy to minimize GC
interference with user activity.

During normal use a high GC threshold is set.  When idling GC is
triggered and a low threshold is set.  The intent is to do as much GC
activity as possible when the user is not interacting with Emacs.

<https://gitlab.com/koral/gcmh>
<http://akrl.sdf.org/#orgc9536b4>

I've "recently" implemented Stefan's idea to compute the idle timer time
based on the last garbage collection time.

The package is on MELPA since ~2 years with I think a decent number of
(I assume happy) users.

Blaming current master I believe the other two contributors are below 10
contributed lines so I think should be copyright assignment wise okay.

Feedback welcome.

Thanks

  Andrea