Switched from using urllib2 to requests.

urllib2 is a security hazzard, it does not perform certificate checks against a trust root by default, nor does it perform service_identity checks.

Also, requests has a prettier API.
Use the older requests API
Set the content-type header and use POST, which the ACME spec requires
Merge pull request #2 from alex/use-requests

Switched from using urllib2 to requests.