Initial version of the same-origin policy model in Alloy

This initial version contains Alloy models of:
* client-server model with HTTP 
* the same origin policy
* the cross-origin sharing 
* security property

To add for the future versions:
* model documentation
* JSONP
* PostMessage
What do you mean by 'dynamic'? Does this provide a clear mechanism to increase the number of possible instances that are generated / checked by the model? Or do they do something to allow a single instance to 'mutate' based on some stimulus?