Added blpop and adjusted to signed 64 bit numbers

Because we're finalizing the Redis API, I thought it would be important to make some better decisions.

First, it's very unsafe for the API to use size_t b/c on i386 platforms forcing 32 bit integers could result in data loss considering Redis sends a string of a 64 bit integers always.

I added ```bblpop``` as a blocking list pop and a non-blocking list ```blpop``` as a task with concurrency. An issue I pointed out earlier was that redis was not precise on its timeout. The suggestion was to close the connection after 10 seconds, but using a task the best workaround would be to run :

```auto value = redis.blpop!(string[])(10.seconds, "list1", "list2").receiveTimeout!string(10.seconds);```
```redis.lpush("list1", "1"); // satisfies the receive loop in blpop``` 

This way, the connection will be recycled and the timeout ends nearer to 10s rather than 10.66s+.

I'd also like to suggest changing the template parameters, ie. ```lindex(T : E[], E)``` should be ```lindex(T)``` b/c there would be more logic requesting the response type rather than specifying the underlying range.