Accelerate model pre-processing and post-processing (#23)

* Add X struct to handle input and preprocessing

*Add Ops struct to manage common operations

* Use SIMD (fast_image_resize) to accelerate model pre-processing and post-processing

examples/rtmo/main.rs

@@ -16,7 +16,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     // run
     let y = model.run(&x)?;
 
-    // // annotate
+    // annotate
     let annotator = Annotator::default()
         .with_saveout("RTMO")
         .with_skeletons(&coco::SKELETONS_16);