true if Windows OS and path begins with slash or backslash.
Examples:
driveRelative("/Users") // true in Windows
, false elsewhere.
driveRelative("\\Users") // true in Windows
, false elsewhere.
driveRelative("C:/Users") // false always
current working drive if Windows, empty string elsewhere. Paths.get(driveRoot) == current working directory on all platforms.
Equivalent to os.Path.apply, but automatically expands a
leading ~/
into the user's home directory, for convenience