rust: Create a root file for modules

The new `lib.rs` file is created to refer to all modules written in Rust. This way, only one `rustc` call is needed to compile an arbitrary amount of modules. It also converges with the way crates are structured.

src/lib.rs

@@ -0,0 +1,3 @@
+#[macro_use]
+mod bitflags;
+mod imservice;