Return result type from syscall and format info on panic.

rust/usr/testbed/src/main.rs

@@ -8,6 +8,7 @@ use mammoth::debug;
 use mammoth::define_entry;
 use mammoth::syscall::debug;
 use mammoth::syscall::z_err_t;
+use mammoth::syscall::Writer;
 
 define_entry!();
 
@@ -17,5 +18,12 @@ pub extern "C" fn main() -> z_err_t {
     let x = Box::new("Heap str");
     debug(&x);
     debug!("Formatted {}", "string");
+    let mut vmmo_cap: u64 = 0;
+    let obj_req = mammoth::syscall::ZMemoryObjectCreateReq {
+        size: 0,
+        vmmo_cap: &mut vmmo_cap as *mut u64,
+    };
+    mammoth::syscall::syscall(mammoth::syscall::kZionMemoryObjectCreate, &obj_req)
+        .expect("Failed to create memory object");
     0
 }