Index option added for change_table migrations

In case if we want to add a column into the existing table
with index on it, we have to add column and index in two
seperate lines.
With this feature we don't need to write an extra line to
add index for column. We can just use `index` option.

Old behaviour in action:
```
  change_table(:languages) do |t|
    t.string :country_code
    t.index: :country_code
  end
```

New behaviour in action:
```
  change_table(:languages) do |t|
    t.string :country_code, index: true
  end
```

Exactly same behaviour is already exist for `create_table` migrations.

1 files changed, 8 insertions, 0 deletions

diff --git a/activerecord/test/cases/migration/change_table_test.rb b/activerecord/test/cases/migration/change_table_test.rb
index 034bf32165..c108d372d1 100644
--- a/activerecord/test/cases/migration/change_table_test.rb
+++ b/activerecord/test/cases/migration/change_table_test.rb
@@ -164,6 +164,14 @@ module ActiveRecord
         end
       end
 
+      def test_column_creates_column_with_index
+        with_change_table do |t|
+          @connection.expect :add_column, nil, [:delete_me, :bar, :integer, {}]
+          @connection.expect :add_index, nil, [:delete_me, :bar, {}]
+          t.column :bar, :integer, index: true
+        end
+      end
+
       def test_index_creates_index
         with_change_table do |t|
           @connection.expect :add_index, nil, [:delete_me, :bar, {}]