0x80 to 0x9F should be dumped by libyaml differently.

They should be dumped as "\u0080", not "\x80". For example, U+0092
needs to be represented as "\u0092" ("\xC2\x92"), not simply "\x92".
These two have completely different meanings.

Realistically, this should be a pullrequest to libyaml, but I am lazy.