Add missing function prototypes.  This avoids implicit function
declarations when building Nilsimsa.xs and build failures with future
compilers.

Submitted upstream: <https://rt.cpan.org/Public/Bug/Display.html?id=145874>

diff --git a/nilsimsa.h b/nilsimsa.h
index 8ebb5f108d615ecb..88f4261841460a8b 100644
--- a/nilsimsa.h
+++ b/nilsimsa.h
@@ -47,6 +47,8 @@ int nilsimsa(struct nsrecord *a,struct nsrecord *b);
 void aggregate(int n);
 void codetostr(struct nsrecord *a,char *str);
 int strtocode(char *str,struct nsrecord *a);
+void makecode(struct nsrecord *a);
+void clear(struct nsrecord *a);
 
 int accbuf(unsigned char *buf,int len,struct nsrecord *a);
 void dprint(char *msg);