Added layer for using symlinks on windows in a portable way. 

Hi Boris,

I added a new file, which allows the user to include the gem and use the symlink as on other systems, which directly support them.

This is simply done by overwrting the 

    File.symlink
    File.symlink?
    File.readlink

functions. I also updated directly the documentation and the version number of the gem. It would be great if you could merge this into your release branch. 

Please let me know if you have questions or change requests. 

Thanks,
\- Lars