integrate platform sub-namespace into source code and documentation

this updates function calls to functions that have been moved from
the utils namepsace or the Info class to platform::

src/NETCDF/dump_netcdf.cpp

@@ -274,7 +274,7 @@ void DumpNetCDF::openfile()
     if (append_flag && !multifile) {
       // Fixme! Perform checks if dimensions and variables conform with
       // data structure standard.
-      if (not utils::file_is_readable(filecurrent))
+      if (not platform::file_is_readable(filecurrent))
         error->all(FLERR, "cannot append to non-existent file {}",filecurrent);
 
       if (singlefile_opened) return;