Removes repetition from method attributes and fixes failing specs

Now on master:

````cs
    public interface IDummyHttpApi
    {
        [Get("/foo/bar/{id}")]
        Task<string> FetchSomeStuff(int id);

        [Get("/foo/bar/{id}?baz=bamf")]
        Task<string> FetchSomeStuffWithHardcodedQueryParameter(int id);
    }
````

With this pull request

````cs
    public interface IDummyHttpApi
    {
        [Get("/bar/{id}")]
        Task<string> FetchSomeStuff(int id);

        [Get("/bar/{id}?baz=bamf")]
        Task<string> FetchSomeStuffWithHardcodedQueryParameter(int id);
    }

    RestService.For<IDummyHttpApi>("http://api.com/foo")
`````

It will spare you from writting `/api/v1` on all your endpoints, making it easier to update to a new api version.