[program_options] parse_config_file documentation bug

[rodrigo_b]

No where in the documentation the expected syntax of the config_file is mentioned.

I found on the code the comment

http://www.google.com/codesearch?hl=en&q=+file:config_file.hpp+show:Zye14269keo:YJNqZ7IaevU:1tGSWV4a4yE&sa=N&cd=4&ct=rc&cs_p=http://spirit.sourceforge.net/dl_more/program_options.zip&cs_f=boost/program_options/config_file.hpp#a0

  /** Standalone parser for config files in ini-line format:

        Config file can not contain arguments.


        - '#' is comment character: it is ignored together with
          the rest of the line.
        - variable assignments are in the form
          name '=' value.
          spaces around '=' are trimmed.
        - Section names are given in brackets.

         The actuall variable name is constructed by combining current section
         name and variable name, with dot between. If section_name already
         contains dot at the end, new dot is not inserted. For example:
         @verbatim
         [gui.accessibility]
         visual_bell=yes
         @endverbatim
         will result in option "gui.accessibility.visual_bell" with value
         "yes" been returned.
     */


Such kind of information should be on the documentation.

[Vladimir Prus]

(In [38495]) Document config file support in more detail. Fixes #808. Fixes #1125.