Adding a block to do operations and close the connection in the end

[fabioperrella]

Hi!

First, great job with this gem, it helped us a lot!

After the merge of #175 , it is possible to use the shutdown method to close the connections, but what about having a method where it is possible to pass a block which will close the connection after yield it?

Example:

client.closing_connection do
  client.logical.read('something')
  client.login.write('something')
end

The implementation would be like this:

def closing_connection
  yield
ensure
  shutdown
end

The code is not 100% correct, it is just to show the ideia.

If you agree, I can send a pull request with this.

Thank you!