Version Bump v3.6.0: sendgrid#234 Substitutions allow non-strings for…

… values

Version Bump v3.5.0: sendgrid#233 Allow dict to be passed to add_headers

Version Bump v3.4.0: Support larger files, up to 20MB for Incoming Parse

Version Bump v3.3.1: Inbound Parse fixes

Version Bump v3.3.0: Pull sendgrid#212 - allow for custom Inbound Par…

…se config.yml

Version Bump v3.2.3: Pull sendgrid#211, updates to inbound parse

Version Bump v3.2.2: Added TOC and USE_CASES.md

Version Bump v3.2.1: pep8, PyPi fixes

Correcting version number

Version v3.1.10: Fix botched 3.1.9 release