Add non-empty test programs.

programs/arithmetic.chalk

@@ -0,0 +1,7 @@
+fun main(): u0 {
+    1+2+3;
+    var a = 5+5;
+    var b = a;
+    var a = a + b;
+    var c = a - b;
+}

programs/call.chalk

@@ -0,0 +1,21 @@
+fun double(a): u8 {
+    return a + a;
+}
+
+fun quadruple(a): u8 {
+    return double(double(a));
+}
+
+fun reuse(): u0 {
+    var one = 2;
+    var two = 4;
+    var three = 6;
+}
+
+fun main(): u0 {
+    var a = quadruple(4);
+    var one = 1;
+    var two = 2;
+    var three = 3;
+    reuse();
+}