Move prelude.schala into separate directory

schala-lang/language/src/schala.rs

@@ -53,7 +53,7 @@ impl Schala {
   /// Creates a new Schala environment with the standard prelude, which is defined as ordinary
   /// Schala code in the file `prelude.schala`
   pub fn new() -> Schala {
-    let prelude = include_str!("prelude.schala");
+    let prelude = include_str!("../source-files/prelude.schala");
     let mut env = Schala::new_blank_env();
 
     let response = env.run_pipeline(prelude);