Aditional validation

* ```Virgilio.prototype.namespace$``` was able to create namespaces without name, so I added namespace name validator to check it. 
* Any Virgilio method or property could be changed with ```Virgilio.prototype.extend$```, including namespaces
Yes, I believe it can be replaced with ```/^\w+(\.\w+)*$/```, and instead of meta ```\w``` can be used range of characters, e.g ```/^[a-zA-Z$][a-zA-Z0-9$]*(\.[a-zA-Z$][a-zA-Z0-9$]*)*$/``` it depends on which characters are allowed in namespace name.