Add params for post requests

This adds support for sending additional parameters and HTTP headers with requests.

Screenshot:
![http-header-and-parameter-additions](https://f.cloud.github.com/assets/283234/2063144/be7615b2-8caf-11e3-890c-ad5c7de2fb83.png)

Would love some code review on this to be sure I am not over complicating things. /cc @jayroh