Dev-env

Added

* add [Jekyl](https://jekyllrb.com/) and [Bundler](https://bundler.io/) to dev-env docker image
* add support for .yamllintignore so run-yamllint.sh can ignore specific files

Changed

* flake8 3.7.9 -> 3.8.3
* pycodestyle 2.5.0 -> 2.6.0
* docker-destructive-cleanup.sh now uses docker container prune
* codecov 2.0.22 -> 2.1.8
* twine 3.1.1 -> 3.2.0
* fixed markdown syntax error in bin/README.md

Removed

* Nothing

Added

* added bin/in-container/get-circle-ci-executor.sh

Changed

* Nothing

Removed

* Nothing

Added

* added bin/get-circle-ci-executor.sh

Changed

* dramatically simplify use of bin/install-dev-env.sh
* replaced bin/check-consistent-dev-env-version.sh
with bin/get-circle-ci-executor.sh
* shellcheck now installed per [these](https://github.com/koalaman/shellcheck/issues/1871)
instructions

Removed

* removed bin/check-consistent-dev-env-version.sh

Added

* [CodeFactor](https://www.codefactor.io) badge to main README.md
* in-container/run-markdownlint.sh actually works now!!!

Changed

* mock 4.0.1 -> 4.0.2
* increased reliability of CircleCI CLI install

Removed

* Nothing

Added

* Nothing

Changed

* mock 4.0.0 -> 4.0.1
* pip3 install -> python3.7 -m pip install
* CircleCI wasn't getting installed because curl -fLSs https://circle.ci/cli | bash
generated curl: (16) Error in the HTTP2 framing layer - resolved by getting
curl to use HTTP 1.1

Removed

* Nothing

Added

* add [codecov](https://codecov.io/)

Changed

* .run-yamllint.sh will now work even if there is no .yamllint
in the repo's root directory

Removed

* Nothing