mruby-array-ext: add a new method Array#fetch_values

mrbgems/mruby-array-ext/test/array.rb

@@ -174,6 +174,13 @@ assert("Array#fetch") do
   assert_raise(IndexError) { a.fetch(100) }
 end
 
+assert("Array#fetch_values") do
+  a = [ 11, 22, 33, 44 ]
+  assert_equal([33, 11], a.fetch_values(2, 0))
+  assert_raise(IndexError) { a.fetch_values(2, 5) }
+  assert_equal([33, 55], a.fetch_values(2, 5) { |i| i*11 })
+end
+
 assert("Array#fill") do
   a = [ "a", "b", "c", "d" ]
   assert_equal ["x", "x", "x", "x"], a.fill("x")