Enhance a few docstrings.

* clojure-mode.el (clojure-defun-style-default-indent)
(clojure-omit-space-between-tag-and-delimiters)
(clojure-space-for-delimiter-p, clojure-no-space-after-tag)
(clojure-mode, clojure-font-lock-def-at-point)
(clojure-font-lock-extend-region-def)
(clojure-font-lock-extend-region-comment, clojure-forward-sexp)
(clojure-defun-indents): Enhance docstring.