Reorganise root exports and update demo

src/bin/demo.rs

@@ -1,15 +1,7 @@
-use deriv::Repl;
-use deriv::eval;
-
 fn main() -> std::io::Result<()> {
-	let eval = deriv::pipeline!(
-		eval::Normaliser::new(),
-		eval::Differentiator::new('x'),
-		eval::ConstFolder::new(),
-		eval::Simplifier::new(),
-		eval::ConstFolder::new(),
-		eval::Canonicaliser::new()
-	);
-	let mut repl = Repl::new(std::io::stdin(), std::io::stdout(), eval);
+	let mut repl = deriv::Repl::new(
+		std::io::stdin(),
+		std::io::stdout(),
+		deriv::evaluator('x'));
 	repl.run()
 }