Merge pull request prometheus#1535 from prometheus/fabxc/0.18.0rc1_ch…

…angelog

Add 0.18.0rc1 changelog

Bump version to 0.17.0

Bump version to 0.17.0rc2

Add changelog for 0.17.0

Update release date in changelog

Cut 0.16.1

Correct date of 0.16.0 release in CHANGELOG.md

Merge pull request prometheus#1130 from prometheus/rc

Cut release 0.16.0rc2

Fix date of 0.16.0rc1 release in CHANGELOG.md.

Merge pull request prometheus#933 from prometheus/cut-0.15.1

Cut Prometheus version 0.15.1.