add generics

test/fixtures/valid/pipeline_precedence.ls

@@ -0,0 +1,5 @@
+add_ten: i32 -> i32: @ value: i32 { value + 10 }
+double: i32 -> i32: @ value: i32 { value * 2 }
+
+# Stages bind tighter than prefix and infix operators: -{3->add_ten} + 2 * {3->double}.
+mixed: i32: -3->add_ten + 2 * 3->double - {1 + 1}->double