The global config object allows values to be set.

  Previously the global configuration object just read settings from
 the configuration file.  Now it allows values to be set
 programattically too.

  We use this fact to pass the include-path option from the command
 line/config file to the global object - where any interested plugins
 can pick it up.
  The plugin-factory passes the global config to all plugins.

  The plugin-factory method 'expandVariables' will now pass an instance
 of the global configuration object to all loaded plugins.

  This allows plugins to determine values such as the include-path.
  Include files come from the include-path now.

  The file-contents plugin will search each directory from the
 include-path, looking for matching values.

  Closes #2.
  All plugins receive an extra argument - the global config.

  The API was updated; no functional changes made.