Merge pull request prometheus#3202 from prometheus/beta5

*: release v2.0.0-beta.5

Merge pull request prometheus#3172 from prometheus/cutbeta4

*: cut 2.0.0-beta.4

Merge pull request prometheus#3162 from prometheus/cutbeta3

*: cut 2.0.0-beta.3

*: cut v2.0.0-beta.2

Merge pull request prometheus#3058 from prometheus/cut-beta1

*: cut 2.0.0-beta.1

Merge pull request prometheus#2937 from prometheus/cutbeta

Cut 2.0.0-beta.0

*: cut v2.0.0-alpha.3

*: cut v2.0.0-alpha.1