Add path package

For testing purposes we need to get the long path of filesystem paths
on Windows machines. By default non-UTF8 syscalls will return the short path
(Ex:"C:\PROGRA~1" instead of "C:\Program Files"). This package exports
previously private functions used in the symlink package to determine the
long path of a file/directory.
It's a good point that samefile only works for existing files.  I'd prefer, actually, if you close the PR, that way we know it's not active any more, and you can always reopen it later.