tools: start fs submodule, add read_subdir

This creates an iterator relative to a RawFd via
nix::dir::Dir over nix::dir::Entrys.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/tools.rs

@@ -25,6 +25,7 @@ pub mod wrapped_reader_stream;
 pub mod common_regex;
 pub mod ticket;
 pub mod borrow;
+pub mod fs;
 
 /// The `BufferedReader` trait provides a single function
 /// `buffered_read`. It returns a reference to an internal buffer. The