Ext feature

1) A first commit is a bugfix. Plugin didn't respect a stripTrailingSlash option when params were provided
before:
```javascript
client.foo.read({ a:1 }); // /foo?a=1
client.foo.read({ a:1 }, { b:2 }); // /foo/?a=b&b=2
```
now all is ok `/foo?a=1&b=2` and so on...
2) A second commit adds an ability to provide an extention for url. For example
```javascript
var client = new $.RestClient('/rest/api/', { stripTrailingSlash: true, ext: '.json'});
///...
client.foo.read(); // /foo.json
client.foo.read(2); // /foo/2.json
```
Now we can use format detection features in some frameworks /foo.json - JSON, /foo.xml - XML and so on