// Returns whether r is fullwidth or not.
// It returns true if the category in East Asian Width is in one of
// "W", "F" or "A".
//
// This is used to calculate character widths on text terminals.
// Fullwidth characters like 'あ' spans 2 column spaces, halfwidth characters
// like 'A' spans 1 column space.
//
// See:
// - UAX #11: East Asian Width http://www.unicode.org/reports/tr11/
// - 東アジアの文字幅 - Wikipedia http://ja.wikipedia.org/wiki/%E6%9D%B1%E3%82%A2%E3%82%B8%E3%82%A2%E3%81%AE%E6%96%87%E5%AD%97%E5%B9%85
eastasianwidth.IsFullwidth(r rune) bool