Support Emoji

 + Added 'E' option into guioptions. 'E' option enables to render Emoji characters using 'Apple Color Emoji' font in MacVim. 'E' option is not set in default, so it doesn't change the current behaviour of MacVim.
 + Changed the range of double wide characters for Emoji. From U+1F000 to U+1FFFD. Ref. http://en.wikipedia.org/wiki/Emoji