added missing header file to repo

+/**
+ * my implementation of a ringbuffer.
+ * It maps a shared memory object twice directly following
+ * thus make it possible to read and write from any
+ * position within the buffer without the nasty wrap
+ * calculations.
+ * This is achived because the same memory region is mapped
+ * at the two addresses.
+ */
+#ifndef __RINGBUFFER_H__
+#define __RINGBUFFER_H__
+
+#include <ctype.h>
+#include <string.h>
+#include <sys/types.h>
+
+#include "class.h"
+
+#define ECBUFOVFL		100
+
+
+CLASS(Cbuf) {
+	char * shm_name;  // shared memory identifier
+
+	char * data;
+	char * mirror;
+
+	size_t bsize;
+	size_t bused;
+
+	size_t write;
+	size_t read;
+};
+
+ssize_t cbufRead(Cbuf, int fd);
+ssize_t cbufWrite(Cbuf, int fd);
+
+char *  cbufGetLine(Cbuf);
+char *  cbufGetData(Cbuf, size_t);
+char *  cbufSetData(Cbuf, const void *, size_t);
+
+char *  cbufGetRead(Cbuf this);
+char *  cbufGetWrite(Cbuf this);
+char *  cbufMemchr(Cbuf this, int c);
+size_t  cbufAddrIndex(Cbuf this, const void * c);
+void    cbufIncRead(Cbuf this, size_t n);
+void    cbufIncWrite(Cbuf this, size_t n);
+size_t  cbufGetFree(Cbuf this);
+char    cbufIsEmpty(Cbuf this);
+void    cbufSkipNonAlpha(Cbuf this);
+
+#endif // __RINGBUFFER_H__
+
+// vim: set ts=4 sw=4: