Disable automatically added square brackets at end of array name

Say I want to post an array of data to a remote source:
```
array = [1,2,3]
Unirest.post "https://www.my-website.com", parameters: { data: array }
```
When I receive the HTTP request on my-website.com, the body of the POST looks like this: `data[]=1&data[]=2&data[]=3`

According to [this StackOverflow post](http://stackoverflow.com/questions/1688599/square-brackets-in-html-form-arrays-just-conventional-or-with-a-meaning), those square brackets are a convention to "address a limitation of PHP, which doesn't generate an array automatically if multiple values with the same name are submitted". All well and good if I'm posting to a PHP server, but if I'm posting to a different kind of server (in my case [NancyFx](http://nancyfx.org/)), I can't easily get that data into an array.

I think it would make sense to get rid of these brackets by default and allow developers using unirest-ruby to post to a PHP server to do something like this:
```
array = [1,2,3]
Unirest.post "https://www.my-website.com", parameters: { "data[]": array }
```

Start at the Unirest.post call and trace how the parameters hash serializes array values for the request body. Confirm the desired behavior with the examples in the issue: brackets should not be added automatically, while an explicitly named key such as "data[]" should remain usable.

Written by the indexing model from the issue text.