add Integer#div and Float#div.

mrbgems/mruby-numeric-ext/mrblib/numeric_ext.rb

+module Integral
+  def div(other)
+    self.divmod(other)[0]
+  end
+end

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

@@ -13,3 +13,11 @@ assert('Integer#chr') do
       assert_raise(RangeError) { 256.chr }
   end
 end
+
+assert('Integer#div') do
+  assert_equal 52, 365.div(7)
+end
+
+assert('Float#div') do
+  assert_float 52, 365.2425.div(7)
+end