clojure-mode.el (clojure-docstring-fill-prefix): New option

* clojure-mode.el (clojure-docstring-fill-prefix): New option.

See https://github.com/clojure-emacs/clojure-mode/issues/241 for a discussion about this.
Bozhidar Batsov <notifications@github.com> writes:

> Perhaps we should generate this dynamically to avoid having to
> restart clojure-mode.

Done in latest PR.