normalise should not alter paths that start with \\?\

From https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx#maxpath :

> They indicate that the path should be passed to the system with minimal modification, which means that you cannot use forward slashes to represent path separators, or a period to represent the current directory, or double dots to represent the parent directory.

My take from this is that whenever `\\?\` is at the beginning of a path, then everything afterward must interpreted literally. Specifically:

- `/` should be understood as a normal character, not a path separator
- `.` and `..` should be understood as normal path segments, not special directories

This means whenever `normalise` sees a path that starts with `\\?\`, it should basically do nothing at all.

As of filepath-1.4.1.0, `normalise "\\\\?\\C:\\.\\Windows/" == "\\\\?\\C:\\Windows\\"`, which is incorrect according to MSDN. Instead, it should remain as is.