Nice interface by classes

I think it would be nice to have something more convenient than bunch of methods like vector_push_back() or queue_pop(), where external pointer is needed as an argument. More readable would be something like vector.push_back(6).

And my proposition is like that:

```

dsVector <- setRefClass("Vector",
fields=c("vec"
),
methods = list(
initialize=function(n=0)
{
vec <<- vector_create(n)

},

push_back=function(obj)
{
vector_push_back(vec, obj)
},

back=function(obj)
{
vector_back(vec)
},

front=function(obj)
{
vector_front(vec)
},

size=function()
{
vector_size(vec)
}

))
```

and usage;

```
vec2 <- dsVector$new(5)
vec2$size()
vec2$push_back(1)
vec2$front()
vec2$back()
```

My only concern is how to make indexer, like "vec2[3] = 5", but I think it is possible in one way or another.

OK, maybe another concern: how to do something like as.character(vector) or print(vector).