Implement printing a list of SysV IPC mqs

What could be improved is when printing the information to use a
better human readable format.

As usual the readme and the man page are both updated.

src/main.rs

@@ -25,6 +25,7 @@ enum PosixCommand {
 #[derive(Clap, Debug)]
 enum SysvCommand {
     Create(sysv::Create),
+    List(sysv::List),
     Unlink(sysv::Unlink),
 }
 
@@ -69,6 +70,7 @@ fn main() -> Result<()> {
         },
         Backend::Sysv(s) => match s {
             SysvCommand::Create(c) => c.run()?,
+            SysvCommand::List(l) => l.run()?,
             SysvCommand::Unlink(u) => u.run()?,
         },
     }