sys/string_utils : new (header-only) module for string utilities
sys/string_utils : new (header-only) module for string utilities

This header-only module provides a `string_utils.h` that currently
only provides the non-standard function `explicit_bzero()` to securely
wipe memory. It may be extended with other utility functions in the
future.

jasonatran/RIOT,ant9000/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,ant9000/RIOT,kaspar030/RIOT,kaspar030/RIOT,jasonatran/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,ant9000/RIOT,miri64/RIOT,ant9000/RIOT,jasonatran/RIOT,ant9000/RIOT,miri64/RIOT,miri64/RIOT,miri64/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,miri64/RIOT,RIOT-OS/RIOT,kaspar030/RIOT