Merge branch 'stable-2.16' into stable-3.0
* stable-2.16:
Bump Bazel version to 2.2.0
Bump required Bazel version to 2.1.0
Upgrade bazlets to latest stable-2.16 to build with 2.16.16 API
Documentation: Refactor to match other plugin documentation
Add an empty tools/BUILD file explicitly for Bazel
Upgrade bazlets to latest stable-2.16
Upgrade bazlets to latest stable-2.16
Upgrade bazlets to latest stable-2.15
Upgrade bazlets to latest stable-2.14
config.md: Correct formatting of config values
Change-Id: I8cc6f59eaf1bc33b9d37b7ec56c74181d9aff4f3