add buffer_init_allocbuf, buffer_init_read, buffer_init_write, buffer_init_read_allocbuf, buffer_init_write_allocbuf

buffer/buffer_init_write_allocbuf.c

@@ -0,0 +1,7 @@
+#include <unistd.h>
+#include "buffer.h"
+
+int buffer_init_write_allocbuf(buffer* b, int fd, size_t ylen) {
+  return buffer_init_allocbuf(b, write, fd, ylen);
+}
+