feat(example): aloow example run at workspace root

examples/mpg_line.rs

@@ -1,15 +1,24 @@
+use std::{env, path::PathBuf};
+
 use gongbi::{aes, geom_line, plot};
 use polars::prelude::*;
 
 fn main() -> anyhow::Result<()> {
+    let examples_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap()).join("examples");
+    let mpg = examples_dir.join("mpg.csv");
+
     let mpg = CsvReadOptions::default()
         .with_has_header(true)
-        .try_into_reader_with_file_path(Some("examples/mpg.csv".into()))?
+        .try_into_reader_with_file_path(Some(mpg))?
         .finish()?;
 
-    let plot = plot!(mpg, aes!(hwy)) + geom_line!(aes!(label = "hwy"));
+    let plot = plot!(mpg.clone(), aes!(hwy)) + geom_line!(aes!(label = "hwy"));
+
+    plot.to_svg(examples_dir.join("mpg_line.svg"), (1024, 768))?;
+
+    let plot = plot!(mpg.clone(), aes!(hwy)) + geom_line!(aes!(shape = 2));
 
-    plot.to_svg("mpg_line.svg", (1024, 768))?;
+    plot.to_svg(examples_dir.join("mpg_line_shape.svg"), (1024, 768))?;
 
     Ok(())
 }