Move `Object#(Rational|Complex)` to `Kernel`

mrbgems/mruby-complex/mrblib/complex.rb

@@ -147,8 +147,10 @@ class << Complex
   alias_method :rect, :rectangular
 end
 
-def Complex(real, imaginary = 0)
+module Kernel
+  def Complex(real, imaginary = 0)
     Complex.rectangular(real, imaginary)
+  end
 end
 
 [Fixnum, Float].each do |cls|

mrbgems/mruby-rational/mrblib/rational.rb

@@ -75,11 +75,13 @@ class Numeric
   end
 end
 
-def Rational(numerator = 0, denominator = 1)
+module Kernel
+  def Rational(numerator = 0, denominator = 1)
     a = numerator
     b = denominator
     a, b = b, a % b until b == 0
     Rational._new(numerator.div(a), denominator.div(a))
+  end
 end
 
 [:+, :-, :*, :/, :<=>, :==, :<, :<=, :>, :>=].each do |op|