Version Bump v3.1.0: PR sendgrid#158, Solves sendgrid#138 [Enhancemen…

…t] allow using custom Client, http proxy support

Version Bump v3.0.9: Added TOC to README, Added USE_CASES.md

Version Bump v2.3.4: Fix Response Charset to UTF-8

Version Bump v3.0.7: Error handling improvements

Version Bump v3.0.6: Added troubleshooting section

Version Bump v3.0.5: README documentation update

Version Bump v3.0.4: Fix for sendgrid#120

Version Bump v3.0.3: Update docs, unit tests and examples to include …

…Sender ID

Version Bump v3.0.2: swagger/oai updates

Version Bump v3.0.1: Added default Accept header