Replace U+XXXX with Unicode character

[pryrt]

Maybe with a checkbox in the OPTIONS dialog, or maybe always on: have a permanent GLOBAL replacement where U+XXXX (for XXXX = 2-6 hexadecimal digits) would be automatically replaced with the appropriate unicode character

(this is at least partially dependent on #14 , because it requires the plugin be able to put Unicode text into the editor with the correct encoding)