Add List.extend and List.to_list, plus some more tests

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tests/list.npp

@@ -0,0 +1,51 @@
+# List type operator and function tests
+
+a = []
+
+println("to_str")
+println(a.to_str())
+println([1, 2, 3])
+println(["a", "b", "c"])
+println(["a\nb\nc"])
+
+println("push and pop")
+a.push(1234)
+a.push(56)
+println(a)
+println(a.pop())
+println(a)
+a.push(99)
+a.push(100)
+println(a)
+a.pop()
+a.pop()
+a.push('99')
+a.push('100')
+println(a)
+
+println("len")
+println(a.len())
+a.pop()
+println(a.len())
+a.pop()
+println(a.len())
+a.pop()
+println(a.len())
+
+println("extend")
+a.extend([1, 2, 3])
+println(a)
+a.extend([1, 2, 3])
+println(a)
+a.extend(['a', 's', 'd', 'f'])
+println(a)
+
+println("constructor")
+println(List("asdf"))
+println(List([1, 2, 3]))
+# ensure that creating a new list actually clones it
+b = [1, 2, 3]
+c = List(b)
+c.pop()
+println(b)
+println(c)