key-chord keyword support for use-package.

With this extension, you can define chords using the :chords keyword in the same manner as :bind and related keywords, using a cons or a list of conses:

(use-package ace-jump-mode
  :chords (("jj" . ace-jump-char-mode)
           ("jk" . ace-jump-word-mode)
           ("jl" . ace-jump-line-mode)))