Fix_#574
Old impl of keyNotation only accepts US keyboard key events.
Key events generated by other keyboard (like Russian) generates
key events with unichar that can not be converted to XVim key notation.
This fix converts such unichar to simply the character of the unichar.
Merge branch 'bugfix/issue_#574' of github.com:JugglerShu/XVim into bugfix/issue_#574

* 'bugfix/issue_#574' of github.com:JugglerShu/XVim:
  Old impl of keyNotation only accepts US keyboard key events. Key events generated by other keyboard (like Russian) generates key events with unichar that can not be converted to XVim key notation. This fix converts such unichar to simply the character of the unichar.