Support plusarg +h/+help option for HTIF

fesvr/htif.cc

@@ -249,7 +249,11 @@ void htif_t::parse_arguments(int argc, char ** argv)
         throw std::invalid_argument("Unknown argument (did you mean to enable +permissive parsing?)");
       case 1: {
         std::string arg = optarg;
-        if (arg == "+rfb") {
+        if (arg == "+h" || arg == "+help") {
+          c = 'h';
+          optarg = nullptr;
+        }
+        else if (arg == "+rfb") {
           c = HTIF_LONG_OPTIONS_OPTIND;
           optarg = nullptr;
         }

fesvr/htif.h

@@ -83,6 +83,7 @@ class htif_t : public chunked_memif_t
 #define HTIF_USAGE_OPTIONS \
 "HOST OPTIONS\n\
   -h, --help               Display this help and exit\n\
+  +h,  +help\n\
        +permissive         The host will ignore any unparsed options up until\n\
                              +permissive-off (Only needed for VCS)\n\
        +permissive-off     Stop ignoring options. This is mandatory if using\n\