Correctly fill the "Authors" section
Various stylistic fixes

* clojure-mode.el (clojure-font-lock-keywords)
(clojure-font-lock-comment-sexp, clojure-mode)
(clojure-font-lock-extend-region-def)
(clojure-mode-font-lock-regexp-groups)
(clojure-find-block-comment-start)
(clojure-font-lock-mark-comment, clojure-indent-function)
(clojure-string-start): Fix docstring indentation and typos.
Fix docstring filling.

* clojure-mode.el (clojure-docstring-fill-column): New option.
(clojure-mode): Set `fill-paragraph-function',
`adaptive-fill-function' and `normal-auto-fill-function'.
(clojure-in-docstring-p): New inline function.
(clojure-adaptive-fill-function): Use it for adaptive filling in
docstrings.
(clojure-fill-paragraph): Fill paragraphs in docstrings.
(clojure-auto-fill-function): Use adaptive filling to determine
fill-prefix.  Use clojure-docstring-fill-column in docstrings.