Releases v0.27 (updates log4j to 2.17.0)

Releases SparkPost lib 0.23

Release for Version 0.22

updates README with current version 0.20

Revs pom version for release to `0.19`

Update README.md

Merge pull request #58 from SparkPost/feature/httpclient_4_5_3_compat…

…_issue57

Feature/httpclient 4 5 3 compat issue57

Releases 0.16.2.

Releasing v0.16.1