More advanced array functionality.

examples/arrays_advanced.fun

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+// Advanced Arrays Demo
+
+// Start with a basic array
+arr = [1, 2, 3]
+print(arr)                       // -> [1, 2, 3]
+
+// length (also works on strings)
+print(len(arr))                  // -> 3
+print(len("hello"))              // -> 5
+
+// push returns new length and mutates the array
+print(push(arr, 99))             // -> 4
+print(arr)                       // -> [1, 2, 3, 99]
+
+// pop returns the removed element and mutates the array
+last = pop(arr)
+print(last)                      // -> 99
+print(arr)                       // -> [1, 2, 3]
+
+// set(array, index, value) sets in place and returns the value
+print(set(arr, 1, 42))           // -> 42
+print(arr)                       // -> [1, 42, 3]
+
+// insert(array, index, value) inserts before index; returns new length
+print(insert(arr, 1, 7))         // -> 4
+print(arr)                       // -> [1, 7, 42, 3]
+
+// remove(array, index) removes at index and returns the element
+removed = remove(arr, 2)
+print(removed)                   // -> 42
+print(arr)                       // -> [1, 7, 3]
+
+// slicing: a[i:j] (end is exclusive), a[i:-1] means to the end
+s1 = arr[1:3]
+print(s1)                        // -> [7, 3]
+s2 = arr[0:-1]
+print(s2)                        // -> [1, 7, 3]
+
+// concatenation with +
+tail = [10, 20]
+combined = arr + tail
+print(combined)                  // -> [1, 7, 3, 10, 20]