added "description" and "readonly" properties to RNA Structs (also accessible via python)

Many descriptions are not written, grep for DOC_BROKEN if you have some spare time to write struct descriptions.

source/blender/makesrna/intern/makesrna.c

@@ -861,6 +861,8 @@ static void rna_generate_struct(BlenderRNA *brna, StructRNA *srna, FILE *f)
 	rna_print_c_string(f, srna->identifier);
 	fprintf(f, ", %d, ", srna->flag);
 	rna_print_c_string(f, srna->name);
+	fprintf(f, ", ");
+	rna_print_c_string(f, srna->description);
 	fprintf(f, ",\n");
 
 	prop= srna->nameproperty;