Add annotate_snippets for better parsing errors (#477)

Adds nicer errors for Podlang code, using the `annotate_snippets` crate, the same crate used by the Rust compiler to generate contextual errors. This prints a short snippet of the code containing the error within the error message, highlighting the part that needs to be fixed.

It also includes a change to the `load_module` function, changing a `Vec` function argument to a slice.

src/frontend/multi_pod/mod.rs

@@ -763,7 +763,7 @@ mod tests {
             "#,
             "test",
             &params,
-            vec![],
+            &[],
         )
         .expect("load module");
         let batch = &module.batch;
@@ -1492,7 +1492,7 @@ mod tests {
             "#,
             "test",
             &params,
-            vec![],
+            &[],
         )
         .expect("load module");
         let batch = &module.batch;
@@ -1621,7 +1621,7 @@ mod tests {
             "#,
             "test",
             &params,
-            vec![],
+            &[],
         )
         .expect("load module");
         let batch = &module.batch;