Fixed symbols/shifted numbers in windows/linux

In linux shift-4 was resolved to 'shift-4' instead of '$' 
Added similar fix as #10 for windows. 

Shifted punctuation also works. 'shift-,' resolves to '<' instead.

This is mainly a pull request to start discussion on the proper way to resolve this issue.  I'm not entirely happy with this fix as I'm not sure if it works across different keyboard layouts.  

CC: atom/vim-mode#222