Add MODNet model (#11)

* Add MODNet for portrait matting

* Minor fixes

* Move assets to home directory

* Add colormap

* ci

* Update README.md

examples/rtmo/main.rs

@@ -3,7 +3,7 @@ use usls::{coco, models::RTMO, Annotator, DataLoader, Options};
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     // build model
     let options = Options::default()
-        .with_model("../rtmo-s-dyn.onnx")
+        .with_model("rtmo-s-dyn.onnx")?
         .with_i00((1, 1, 8).into())
         .with_nk(17)
         .with_confs(&[0.3])