string.strtok should return CString, not CChar

[rwhaling]

I was having trouble getting string.strtok to work right, and noticed it's return type is CChar -- since the C function returns char *, I think that should be CString, instead?
http://man7.org/linux/man-pages/man3/strtok.3.html

#include <string.h>

       char *strtok(char *str, const char *delim);

I'll quickly submit a one-line patch now with the change, but I'm happy to write a unit test if that's merited.

[densh]

Fixed in #656