Buffers for UTF-8 strings.

create n creates the buffer with the initial size n-bytes.

contents buf returns the contents of the buffer.

Empty the buffer, but retains the internal storage which was holding the contents

Empty the buffer and de-allocate the internal storage.

Add one Unicode character to the buffer.

Add the UTF-8 string to the buffer.

add_buffer b1 b2 adds the contents of b2 to b1. The contents of b2 is not changed.