Merge pull request google#1185 from google/rev-0.23

Revise to 0.23.0.

Merge pull request google#1154 from google/rev-0.22.4

Revise to 0.22.4.

Merge pull request google#1131 from google/rev-0.22.3

Revise to 0.22.3.

Merge pull request google#1122 from google/rev-0.22.2

Revise to 0.22.2.

Merge pull request google#1110 from bsilver8192/subclass-std

Fix and test subclasses with C++ std in scope

Merge pull request google#1071 from google/rev-0.22.0

Revise to 0.22.0.

Merge pull request google#1050 from google/rev-0.21.2

Revise to 0.21.2.

Merge pull request google#1047 from google/rev-0.21.1

Revise to 0.21.1.

Merge pull request google#1030 from google/rev-0.21

Revise to 0.21.0.

Merge pull request google#1027 from google/rev-0.20.1

Upgrade to 0.20.1.