Ability to access complete set of client options.

Hello!

Often there is the need to create a new connection to Redis on the basis of existing.
For example, to create a writing session and maintain the ability to read at the time of the transaction.

Because there is no such possibility, it is necessary to use the following method:
```ruby
def write_session
  @write_session ||= ::Redis.new(
    :host    => main_redis.client.host,
    :port    => main_redis.client.port,
    :db      => main_redis.client.db,
    :timeout => main_redis.client.timeout
  )
end
```

But this method does not copy all properties, since they are not available.
For example you can not copy the property "driver."

I would like to have a method of making a copy of connection or (and) to be able to access all the properties of the connection.

Then I could write the following code:
```ruby
  def write_session
    @write_session ||= ::Redis.new(main_redis.client.options)
  end
```
or even:
```ruby
def write_session
  @write_session ||= main_redis.client.clone_connection
end
```

This pull request makes available a a complete set of client options.