restructure: move el compiler content into lang/

lang/tests/calendar/examples/mars-calendar.el

@@ -0,0 +1,21 @@
+// mars-calendar.el — MarsCalendar uses sol period 88775.244 seconds.
+// Two instants exactly one sol apart should differ by 1 in sol number.
+
+fn run_test() -> Int {
+    let cal: Calendar = mars_calendar()
+    let base: Instant = unix_seconds(0)
+    // 88775.244 s * 1e9 nanos = 88775244000000 nanos
+    let one_sol_ns: Int = 88775244000000
+    let one_sol: Duration = el_duration_from_nanos(one_sol_ns)
+    let later: Instant = base + one_sol
+    let ct1: CalendarTime = in_calendar(base, cal)
+    let ct2: CalendarTime = in_calendar(later, cal)
+    let sol1: String = cal_format(ct1, "%sol")
+    let sol2: String = cal_format(ct2, "%sol")
+    let diff: Int = str_to_int(sol2) - str_to_int(sol1)
+    return diff
+}
+
+fn main() -> Void {
+    println(int_to_str(run_test()))
+}