Fix Windows support

[tkadur]

The only thing blocking it from compiling on Windows is a call to std::os::unix::fs::symlink in the linker. This is easily fixable. In particular, the following function needs to be implemented for Windows:

dotman/src/linker/mod.rs

Lines 45 to 48 in efb0192

	#[cfg(unix)]
	fn symlink(source: impl AsRef<Path>, dest: impl AsRef<Path>) -> io::Result<()> {
	std::os::unix::fs::symlink(source, dest)
	}

As for testing that all behavior is correct on Windows, see #2.

[tkadur]

This is really more of a bug, since Windows support has always been intended but not implemented.