add support for Unicode planes and characters above U+FFFF

Looking at QChar code, Qt treats Unicode characters as 16-bit numbers, effectively restricting the range of characters to BMP (Plane 0 of Unicode). I suggest adding support for characters in other planes, beyond U+FFFF. Especially planes 1 and 2 have characters that people sometimes use.

http://en.wikipedia.org/wiki/Mapping_of_Unicode_character_planes