[R6RS] Codecs and endianness

[Michael Sperber]

I only now consciously noticed that Will removed the UTF-xxBE/UTF-xxLE
codecs from the I/O library.  I have no idea why he did
this---presumably because of some interpretation of the Unicode
standard.  However, UTF-16BE/LE are official Unicode encoding schemes
(as per section 2.6 of the Unicode standard), and separate from UTF-16
(with or without BOM).  Therefore, I'd like to add it back, and specify
that the UTF-16 codec deals with an optional BOM on input (defaulting to
UTF-16BE if it's absent), and outputs a BOM on output.

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla