Implement info command for SysV IPC mqs

The `list` command was refactored a little bit as well and the man
page and readme were updated.

src/main.rs

@@ -25,6 +25,7 @@ enum PosixCommand {
 #[derive(Clap, Debug)]
 enum SysvCommand {
     Create(sysv::Create),
+    Info(sysv::Info),
     List(sysv::List),
     Unlink(sysv::Unlink),
 }
@@ -70,6 +71,7 @@ fn main() -> Result<()> {
         },
         Backend::Sysv(s) => match s {
             SysvCommand::Create(c) => c.run()?,
+            SysvCommand::Info(i) => i.run()?,
             SysvCommand::List(l) => l.run()?,
             SysvCommand::Unlink(u) => u.run()?,
         },