Currently the only supported encoding is "ISO8859_1". The SList, Sexp and
SimpleString classes, however, contains hooks to support conversion from and to
any Java-supported byte-representation of strings. Each of these classes
contain the following strings defined:

    protected static String default_encoding = "ISO8859_1";
    public String string_encoding = default_encoding;
    public String byte_encoding = default_encoding;

The String <default_encoding> is a class variable that specifies, surprise,
surprise, the default encoding.

The String <string_encoding> is the encoding used for converting strings to byte
arrays.

The String <byte_encoding> is the encoding used for converting byte-arrays to
strings.

In a fictious case where some utilitizing class knew a certificate in transport
representation originally had its Unicode string data converted to UTF-8
encoded byte arrays, instead of the default ISO8859_1 encoding, this
utilitizing class could specify that the <byte_encoding> was "UTF_8". Vice
versa, to write certificate in UTF_8 transport encoding, <string_encode> would
have to be set to "UTF_8". Note that this should _only_ be done on
Sexp and SimpleString classes that are known to contain only text data. It
would probably not be a good idea to UTF-8 encode a BigInterger.

The SPKI drafts and specifications states that the character encoding should be
Latin-1 (ISO8859-1), so that's why ISO8859_1 is default.
