Add symlink support (Fixes #42)

It's missing the option for relative symlinking, but this should hopefully do the trick for now. Merry Xmas!
I had actually first had it return the original files, untouched, after the symlinks were created, but considering the two possibilities, either return the original file or the new symlink, the latter seemed to behave more like `dest` (since dest returns the newly written file) which would be "least surprising" for the user.