Support no_std in roto-runtime

Add #![no_std] to the runtime crate and introduce optional std and
alloc features. Update the code generator to be compatible and add a
no_std_test example. Remove the generator binary.

Cargo.toml

@@ -6,8 +6,15 @@ members = [
     "benches",
     "roto-tonic",
     "examples/hello_world",
+    "examples/no_std_test",
 ]
 
 exclude = [
     "test_gen_project"
 ]
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"