Reworks workflows into script (#661)

* Reworks some workflows to run a script instead

Advantages are:
- Only one set of tests needs maintenance.
- Local results match workflows, no surprises.
- Reduced reliance on GitHub actions.

Fixes #50, #168, #169, #171, #507

* Adds macos to the test matrix

tools/run_pylint.sh

@@ -1,21 +0,0 @@
-#!/usr/bin/env bash
-# Copyright 2019 Google LLC
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Ensure we are at the project root directory
-cd $(readlink -f $(dirname $0))/..
-
-export PATH="py_virtual_env/bin:$PATH"
-
-pylint --score=n `git ls-files --deduplicate --exclude-standard --full-name '*.py'`