Packaging fix

New upload system -- twine

Version Bump v3.1.0: Hacktoberfest Updates

Version Bump v3.0.0: replaces error handling via HTTPError

Version Bump v2.4.0: sendgrid#19 Added support for slash. Created to_…

…dict property in response object and exception class.

Version Bump v2.3.0: sendgrid#17 Added support for error handling

Version Bump v2.2.1: When Content-Type is not application/json, do no…

…t JSON encode the request body

Version Bump v2.2.0: Ability to set the Content-Type header

Version Bump: v2.1.1: Pull request sendgrid#11

Version Bump 2.1.0: Automatically add Content-Type: application/json …

…when there is a request body