restructure: move el compiler content into lang/

lang/tests/time/examples/time-arithmetic.el

@@ -0,0 +1,20 @@
+// time-arithmetic.el — Instant + Duration -> Instant, then Instant - Instant
+// -> Duration. The codegen routes each BinOp through the typed wrappers
+// (el_instant_add_dur, el_instant_diff). Returns 1 if the elapsed span is at
+// least 5 minutes, 0 otherwise. Because the two now() calls are very close
+// together, the span is very nearly 5.minutes, so >= 5.minutes holds.
+
+// `test` is reserved; using `run_test` instead.
+fn run_test() -> Int {
+    let later: Instant = now() + 5.minutes
+    let span: Duration = later - now()
+    if span >= 5.minutes {
+        return 1
+    } else {
+        return 0
+    }
+}
+
+fn main() -> Void {
+    println(int_to_str(run_test()))
+}