Added ability to use config object

I'm using this gem in a Rails application, and I wanted to be able to set the ID and vCode somewhere other than in the model I was using EAAL.

I have added a config object that allows for key value pairs to be stored in it. The API initialize function now uses the values in the config if they are set. Because it is now possible to call API.new without any parameters, I raise an exception if keyid or vcode is not set.

Example configuration looks like this:

EAAL.config.keyid = 'xxxxxxx'
EAAL.config.vcode = 'xxxxxxxxxxxxxxxxxxxxx'