Modified to use requests

1. AFAIK everyone who had used urllib moved to requests.
2. Requests code is cleaner than urllib.
3. Added example to post source code from raw string.

Issues with old code:
----
1.  `source = open('sample.c').read()` file was opened but never closed.

Suggestion:
---
1. Whenever `run` url is hit and `compile_status` is 'OK', new resource is created(`u'web_link': u'http://code.hackerearth.com/26c372Q'`). Ideally response code should be `201` rather than 200. `200` is also correct, better one is `201`. https://en.wikipedia.org/wiki/List_of_HTTP_status_codes#2xx_Success