tools: add Tied value

Tie two dependent values together, such as a nix::Dir with
its nix::dir::Iter<'a> where 'a is tied to the Dir's
lifetime, making it otherwise impossible to return them or
store them in a struct.

Alternatively we could try the 'rental' crate.

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

src/tools.rs

@@ -24,6 +24,7 @@ pub mod wrapped_reader_stream;
 #[macro_use]
 pub mod common_regex;
 pub mod ticket;
+pub mod borrow;
 
 /// The `BufferedReader` trait provides a single function
 /// `buffered_read`. It returns a reference to an internal buffer. The