[DOC] itemize values for half option of Float#round.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57133 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

numeric.c

@@ -2224,11 +2224,12 @@ rb_int_truncate(VALUE num, int ndigits)
  *     34567.89.round(3)  #=> 34567.89
  *
  *  If <code>half:</code> optional keyword is given, just-half number
- *  will be rounded according to that value.  If it is
- *  <code>:up</code> or +nil+, the result will be rounded up, or it is
- *  <code>:even</code>, the result will be rounded to nearest even
- *  number, or it is <code>:down</code>, the result will be rounded
- *  down.
+ *  will be rounded according to that value.
+ *  Supported values for this keyword are follows.
+ *
+ *  * <code>:up</code> or +nil+: the result will be rounded away from zero
+ *  * <code>:even</code>: the result will be rounded to nearest even number
+ *  * <code>:down</code>: the result will be rounded close to zero
  */
 
 static VALUE