update include file conventions since we no longer require C++98 for LAMMPS core files

doc/include-file-conventions.md

@@ -49,22 +49,15 @@ include files provided with LAMMPS are included with double quotes
 
 For headers declaring functions of the C-library, the corresponding
 C++ versions should be included (examples: `#include <cstdlib>` or
-`#include <cctypes>`).  However, these includes are limited to those defined
+`#include <cctypes>` instead of `#include <stdlib.h>` or
-in the C++98 standard.  Some files thus must use the older style until
+`#include<ctypes.h>` ).
-the minimum C++ standard requirement of LAMMPS is lifted to C++11 or
-even beyond (examples: `#include <stdint.h>` versus `#include <cstdint>`
-or `#include <inttypes.h>` versus `#include <cinttypes>`).
 
 ### C++ Standard Compliance
 
-LAMMPS core files currently correspond to the C++98 standard. Files
+LAMMPS core files use standard conforming C++ compatible with the
-requiring C++11 or later are only permitted in (optional) packages
+C++11 standard, unless explicitly noted.  Also, LAMMPS uses the C-style
-and particularly packages that are not part of the list of commonly
+stdio library for I/O instead of iostreams.  Since using both at the
-used packages such as MOLECULE, KSPACE, MANYBODY, or RIGID.
+same time can cause problems, iostreams should be avoided where possible.
-
-Also, LAMMPS uses the C-style stdio library for I/O instead of iostreams.
-Since using both at the same time can cause problems, iostreams should
-be avoided where possible.
 
 ### Lean Header Files