Version Bump v5.2.0: sendgrid#335: Permit unicode string values with …

…Substitution helper

Version Bump v5.1.0: Pull sendgrid#338, Solves sendgrid#292 __str__

Version Bump v5.0.1: Pull sendgrid#337, fixes issue sendgrid#366: Val…

…ue Error

Version Bump v5.0.0: fixes sendgrid#328 and sendgrid#321

Version Bump v4.2.1: Issue sendgrid#321: Installing 4.2.0 installs th…

…e wrong version of python-http-client

Version Bump: v4.2.0: Pull sendgrid#318 Add ability to reset request …

…headers on client attribute

Version Bump v4.1.0: Pull sendgrid#314 Add ability to impersonate sub…

…user

Version Bump v4.0.0: BREAKING CHANGE sendgrid#244

Version Bump v3.6.5: sendgrid#300 Exclude test package

Version Bump v3.6.4: sendgrid#250 Improve code quality