add binary data structure definitions and image writer function prototypes

src/write.h

@@ -0,0 +1,22 @@
+#ifndef WRITE_H_
+#define WRITE_H_
+
+#include "status.h"
+
+#include <stdint.h>
+#include <stdio.h>
+
+struct ec3_writer;
+struct ec3_tag_writer;
+
+extern enum ec3_status ec3_writer_create(void);
+extern void ec3_writer_destroy(struct ec3_writer *w);
+extern void ec3_writer_write_image(struct ec3_writer *w, FILE *fp);
+
+extern enum ec3_status ec3_writer_create_tag(
+	struct ec3_writer *w,
+	uint32_t tag_type,
+	uint64_t tag_ident,
+	struct ec3_tag_writer **out_writer);
+
+#endif