Describe Fixnum and Bignum integration in NEWS.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55030 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -46,6 +46,8 @@ with all sufficient information, see the ChangeLog file or Redmine
   * Integer#ceil, Integer#floor, and Integer#truncate now take an optional
     digits, as well as Integer#round.  [Feature #12245]
 
+  * Fixnum and Bignum are unified into Integer  [Feature #12005]
+
 * String
 
   * String.new(capacity: size) [Feature #12024]
@@ -84,6 +86,17 @@ with all sufficient information, see the ChangeLog file or Redmine
   Ruby's sum method should be mostly compatible but it is impossible to
   be perfectly compatible with all of them.
 
+* Fixnum and Bignum are unified into Integer  [Feature #12005]
+  Fixnum class and Bignum class is removed.
+  Integer class is changed from abstract class to concrete class.
+  For example, 0 is an instance of Integer: 0.class returns Integer.
+  The constants Fixnum and Bignum is bound to Integer.
+  So obj.kind_of?(Fixnum) works as obj.kind_of?(Integer).
+  At C-level, rb_cFixnum and rb_cBignum is same as rb_cInteger.
+  So, class based dispatch, such as klass == rb_cFixnum and
+  klass == rb_cBignum, should be changed to FIXNUM_P(obj) and
+  RB_TYPE_P(obj, T_BIGNUM).
+
 === Stdlib compatibility issues (excluding feature bug fixes)
 
 * Time