support iterable query params

issue #55 

ex.

```java
@RequestLine("GET /?1={1}&2={2}") // or jaxrs equiv if using feign-jaxrs
Response queryParams(@Named("1") String one, @Named("2") Iterable<String> twos);
```

called with

```java
api.queryParams("user", Arrays.asList("apple", "pear"));
```

would send

```
GET /?1=user&2=apple&2=pear HTTP/1.1
```