Edited Feature: Add support to Destroy a Block [2268]

Hi,

Every endpoint of the Twitter API will be implemented when Tweetinvi 1.0 will be released. Until such time, please feel free to contact me (from discussion or issues to let me know the features you need).

As a result I will implement the feature in next version of Tweetinvi (0.9.4.0).
Until such time, please use the following code:

``` c#
var user = User.GetUserFromId(101010);
var query = string.Format("https://api.twitter.com/1/blocks/destroy.json?user_id={0}", user.Id);
var blockSuccessfullyDestroyed = TwitterAccessor.TryExecutePOSTQuery(query);
```

Linvi