Use mod files

To have things more self contained.

src/posix/mod.rs

@@ -0,0 +1,13 @@
+mod create;
+mod info;
+mod list;
+mod recv;
+mod send;
+mod unlink;
+
+pub use create::Create;
+pub use info::Info;
+pub use list::List;
+pub use recv::Recv;
+pub use send::Send;
+pub use unlink::Unlink;