Convert argument to Katakana and return that.
The argument may be a character or string. The result has the same type.
The argument object is not altered--the value is a copy.
Optional argument HANKAKU t means to convert to `hankaku' Katakana
(`japanese-jisx0201-kana'), in which case return value
may be a string even if OBJ is a character if two Katakanas are
necessary to represent OBJ.
(fn OBJ &optional HANKAKU)