char* strtok_P(char *s, PGM_P delim)
strtok_P() parses the string s
into tokens. The first call to strtok_P() should have s as its first
argument. Subsequent calls should have the first argument set to NULL. If a token ends
with a delimiter, this delimiting character is overwritten with a '\0' and a pointer to
the next character is saved for the next call to strtok_P(). The delimiter string delim may be
different for each call.
The strtok_P() function is similar to strtok() except that delim is pointer to a
string in program space.
The strtok_P() function returns a pointer to the next token or NULL when no more tokens are found.
strtok_P() is NOT reentrant. For a reentrant version of this function see strtok_rP().