List.clear and List.insert().

test/list/clear.wren

@@ -0,0 +1,7 @@
+var a = [1, 2, 3]
+a.clear
+io.write(a)       // expect: []
+io.write(a.count) // expect: 0
+
+// Returns null.
+io.write([1, 2].clear) // expect: null

test/list/insert.wren

@@ -0,0 +1,44 @@
+// TODO(bob): What happens if the index isn't an integer?
+// TODO(bob): Out of bounds.
+
+// Add to empty list.
+var a = []
+a.insert(1, 0)
+io.write(a) // expect: [1]
+
+// Normal indices.
+var b = [1, 2, 3]
+b.insert(4, 0)
+io.write(b) // expect: [4, 1, 2, 3]
+
+var c = [1, 2, 3]
+c.insert(4, 1)
+io.write(c) // expect: [1, 4, 2, 3]
+
+var d = [1, 2, 3]
+d.insert(4, 2)
+io.write(d) // expect: [1, 2, 4, 3]
+
+var e = [1, 2, 3]
+e.insert(4, 3)
+io.write(e) // expect: [1, 2, 3, 4]
+
+// Negative indices.
+var f = [1, 2, 3]
+f.insert(4, -4)
+io.write(f) // expect: [4, 1, 2, 3]
+
+var g = [1, 2, 3]
+g.insert(4, -3)
+io.write(g) // expect: [1, 4, 2, 3]
+
+var h = [1, 2, 3]
+h.insert(4, -2)
+io.write(h) // expect: [1, 2, 4, 3]
+
+var i = [1, 2, 3]
+i.insert(4, -1)
+io.write(i) // expect: [1, 2, 3, 4]
+
+// Returns.inserted value.
+io.write([1, 2].insert(3, 0)) // expect: 3