message: [doc] Handle robocopy exit codes
  Robocopy uses exit codes 0-7 to convey details about what was copied.
  Exit code 8 starts the range of errors.
  Only fail if robocopy exits with a value greater than or equal to 8.
diff: robocopy ..\html . /E /J /MIR /MT /NFL /XD .git 2>&1
  - if ($LASTEXITCODE -ne 0) { throw "Robocopy documentation failed: $LASTEXITCODE" }
  + # Robocopy uses exit codes 0-7 to convey details about
  + # what was copied. Exit code 8 starts the range of
  + # errors.
  +
  + if ($LASTEXITCODE -ge 8) { throw "Robocopy documentation failed: $LASTEXITCODE" }
  git add --all .
  