This version takes about 1/300 of the time of the shell version
and fixes several errors in the output, most importantly that
option descriptions were being truncated at the first empty line.
Because help2doc is run only from make update-man, and the distributed
tarballs include prebuilt man pages, people building ELinks need not
have Perl installed.
This simplifies help2doc since it now just have to do one single thing with
output of either --config-help or --long-help. The new manpage is not as
fancy wrt. indentation and sub titles but it is more uniform and we get a
HTML version.
Generate options-{config,command}.txt with help2doc. Only conditionally
check for API header files, to speed up execusion.
