By adding events of the form (cons t event) to unread-command-events, Emacs
correctly updates this-command-keys for the subsequent use of the prefix.
Before this change, packages like my which-key were not getting the correct
prefix after use-package-autoload-keymap loaded the relevant package.
See https://github.com/justbur/emacs-which-key/issues/192
bind-key supports the keyword ":package" but use-package does not know that. Adding this should be helpful. In the future, maybe we could automatically fill in with the use-package package, but that could be a breaking change.
This change adds a new extension hook `use-package-autoloads/<KEYWORD>` for
specifying exactly which autoloads a keyword should imply. This is the proper
way to indicate autoloads, rather than adding to the `:commands` entry as was
done before.
Further, autoloading now must occur in order to cause implied deferred
loading; if :bind is used with only lambda forms, for example, this will not
cause deferred loading without `:defer t`.
