Add support for Eask files

[Alhadis]

Description

Eask is a CLI for managing Emacs Lisp dependencies, and is intended to replace Cask for managing Elisp projects. Like Cask, it uses a similarly-named Elisp file named Eask, which is the spiritual equivalent of Ruby's Gemfiles (meaning it's very much a one-file-per-repository type of format).

Inexplicably, both Cask and Eask define their own modes for their respective files (despite both containing ordinary Emacs Lisp code), so modelines like -*- mode: eask; -*- have to be considered.¹ I've therefore added their names to Emacs Lisp's aliases list for the benefit of Linguist's Modeline strategy.

Checklist

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories.
    ~788 search results for Eask as of this writing.
  • I have included a real-world usage sample.
    Source: emacs-php/composer.el/Eask
    License: GPL-3.0-or-later²

Footnotes

1. See auto-complete's Eask for a real-world example. ↩

2. I couldn't find a non-GPL sample, and this is the same source that provided our existing Cask filename sample back in Add Cask file as Emacs Lisp #3416. Hence I'm assuming copyleft won't be a problem). ↩