* Extended the Restconf implementation with a limited www-data

* This is an experimental implementation
  * Added `www-data` feature and two new config options to clixon-config.yang:
     * `CLICON_WWW_DATA_PATH`
     * `CLICON_WWW_DATA_ROOT`
  * The limited implemtation is as follows:
     * path: Local files within `CLICON_WWW_DATA_ROOT`
     * operation GET, HEAD, or OPTIONS
     * query parameters not supported
     * indata should be NULL (no write operations)
     * Limited media: text/html, JavaScript, image, and css
     * Authentication as restconf
Generic changes:
  * Uniform path selection across fcgi, native http/1 + http/2

apps/restconf/restconf_root.h

@@ -53,6 +53,7 @@
 /*
  * Prototypes
  */
+int api_path_is_restconf(clicon_handle h);
 int api_well_known(clicon_handle h, void *req);
 int api_root_restconf(clicon_handle h, void *req, cvec *qvec);