Merge pull request #220 from darrensmith223/add-perf-substitution

Added support for perform_substitutions transmissions option

Version 1.3.9

Version 1.3.9

Merge pull request #214 from darrensmith223/patch-1

add-amp-html

Merge pull request #190 from SparkPost/vulnerable_dep

Bump version to 1.3.7

Tagging v1.3.6 based on commit that changed version in setup.py

Merge pull request #143 from rajumsys/v1.3.5

v1.3.5 release prep

Bump version, update changelog

Bump version, update changelog

Bump version, update changelog