Remove errors package, add comments and simplify. (#2925)

vendor/github.com/pkg/errors/appveyor.yml

@@ -1,32 +0,0 @@
-version: build-{build}.{branch}
-
-clone_folder: C:\gopath\src\github.com\pkg\errors
-shallow_clone: true # for startup speed
-
-environment:
-  GOPATH: C:\gopath
-
-platform:
-  - x64
-
-# http://www.appveyor.com/docs/installed-software
-install:
-  # some helpful output for debugging builds
-  - go version
-  - go env
-  # pre-installed MinGW at C:\MinGW is 32bit only
-  # but MSYS2 at C:\msys64 has mingw64
-  - set PATH=C:\msys64\mingw64\bin;%PATH%
-  - gcc --version
-  - g++ --version
-
-build_script:
-  - go install -v ./...
-
-test_script:
-  - set PATH=C:\gopath\bin;%PATH%
-  - go test -v ./...
-
-#artifacts:
-#  - path: '%GOPATH%\bin\*.exe'
-deploy: off