Updated CHANGELOG for 0.20.1-rc3.

Updated CHANGELOG for 0.20.1-rc3.

Updated configure.ac to 0.20.1.

*** MODIFIED for 0.20.1-rc1 *** Added CHANGELOG for 0.20.1.

Fixed a bug in docker/docker.cpp that causes unresolved symbols on OSX.

Review: https://reviews.apache.org/r/24825

Fixed a bug in docker/docker.cpp that causes unresolved symbols on OSX.

Review: https://reviews.apache.org/r/24825

Fixed style issues in CHANGELOG.

Updated version to 0.19.1.

Updated version to 0.19.1.

Updated CHANGELOG for 0.19.0.