Remove pub declarations and move to posix::*

This is in order to prepare also for SysV message queues.

src/posix.rs

@@ -0,0 +1,11 @@
+mod create;
+mod info;
+mod recv;
+mod send;
+mod unlink;
+
+pub use create::Create;
+pub use info::Info;
+pub use recv::Recv;
+pub use send::Send;
+pub use unlink::Unlink;