Improvements

Error handling for credential retrieval, file I/O and auth
Removing redundant use of pytz; using UTC for everything
Replacing urllib2 with Requests, because really now
Adding some feedback, which is printed to stdout
Check that the credential format is OK
Slightly friendlier IOError message
Tidying up

Auth credentials are now read directly into the payload dict
Only the first line of the credentials file is read
Bookmarks are separately retrieved and written to file
Updating Readme with correct line number
Merge pull request #1 from urschrei/master

Add some feedback, error handling, and use Requests instead of urllib2