No logging after upgrading to Savon 2

Global configuration have been disabled in Savon 2 so it is not possible to set logging options in rconomic. So i would like to make a patch to get the loggin functionality back.

Logging can be configured in Savon with a block syntax a simple assigments.

Configuring with the block syntax:
```ruby
Economic::Session.new(aggr_number, usr, pswd) do |config|
  config.log = true
  config.logger = Rails.logger
  config.log_level = :info
end
```

Configuring with assignments:
```ruby
session = Economic::Session.new(aggr_number, usr, pswd)
session.log_level = :info
session.logger = Rails.logger
session.log = true
```