Make the description of the library more

Make the description of the library more
accurate.
(lm-any-header): New user option.
(lm-section-start): New function; rewrite of `lm-section-mark'.
(lm-section-mark): Make alias of `lm-section-start'.
(lm-section-end): New function.
(lm-code-start): New function; rewrite of `lm-code-mark'.
(lm-code-mark): Make alias of `lm-code-start'.
(lm-commentary-start): New function; rewrite of
`lm-commentary-mark'.
(lm-commentary-mark): Make alias of `lm-commentary-start'.
(lm-commentary-end): New function.
(lm-history-start): New function; rewrite of `lm-history-mark'.
(lm-history-mark): Make alias of `lm-history-start'.
(lm-commentary): Use `lm-commentary-end' to find the end of the
commentary section.