Implement the Circle CI configuration file

Circle CI (1) is one of the most popular and proven CI providers that
allows to automate pipelines from commit to deploy with a quick, safe,
and scaled process. They support many languages and provide great and
unique features like orbs (2), job orchestration, powerful caching, SSH
or local builds for easy debugging and first-class Docker and GitHub
integration (apps, hooks, etc.) support.
The extensive and well-written documentations (3) make it easy to set
up and configure it for the usage in projects.
Circle CI has been used for almost all open source projects of Arctic
Ice Studio and will be used as primary CI provider for _Nord Docs_ too.

Before starting to run builds, Circle CI must be authorized on a per
project basis to access the code on GitHub. After the process has been
authorized (GitHub OAuth) the project will be added to the dashboard and
required webhooks to listen for new Git events will be automatically set
up. See the documentation about how to get started and add a project to
the dashboard (4).
NOTE: The latest config 2.1 features (5) are currently still in Beta
Preview and must be enabled explicitly for each project via Settings ->
Advanced Settings -> "Enable build processing (preview)"! See the
"Enabling Build Processing" (6) documentation for more details.

The Docker image of the CI container (7) will be the currently latest
stable Node.js (8) LTS version `10.x.x` and the previous LTS version
`8`. The `-browsers-legacy` tag suffix (9) can
be used later on for end-to-end tests (GH-38) with Cypress (10). Next to
Node.js these images currently include Chrome, Firefox, Java 8, and
PhantomJS.

To gather and upload all created coverage reports the
"codecov/codecov" (11) Circle CI orb (12) which provides the `upload`
command for easy integration into jobs and workflows.

References:
  (1) https://circleci.com
  (2) https://circleci.com/orbs
  (3) https://circleci.com/docs
  (4) https://circleci.com/docs/2.0/first-steps
  (5) https://github.com/CircleCI-Public/config-preview-sdk/blob/master/docs/README.md
  (6) https://circleci.com/docs/2.0/build-processing
  (7) https://hub.docker.com/r/circleci/node/tags
  (8) https://nodejs.org
  (9) https://circleci.com/docs/2.0/circleci-images/#language-image-variants
  (10) https://www.cypress.io
  (11) https://circleci.com/orbs/registry/orb/codecov/codecov
  (12) https://circleci.com/docs/2.0/orb-intro

GH-44

.circleci/config.yml

@@ -0,0 +1,118 @@
+# Copyright (C) 2018-present Arctic Ice Studio <development@arcticicestudio.com>
+# Copyright (C) 2018-present Sven Greb <development@svengreb.de>
+#
+# Project:    Nord Docs
+# Repository: https://github.com/arcticicestudio/nord-docs
+# License:    MIT
+
+# Configuration for Circle CI.
+#
+# References:
+# - https://circleci.com/docs/2.0
+# - https://circleci.com/docs/2.0/circleci-images
+
+version: 2.1
+
+commands:
+  build:
+    description: "Build a production bundle with Gatsby"
+    steps:
+      - run:
+          name: Build production bundle
+          command: npm run build:gatsby
+  post-process:
+    description: "Post-process the build"
+    steps:
+      - save-npm-cache
+      - store_artifacts:
+          path: ./build/reports
+      - store_artifacts:
+          path: ./public
+      - store_artifacts:
+          path: ./node_modules.tgz
+      - codecov/upload:
+          file: ./build/reports/coverage
+  pre-process:
+    description: "Pre-process the build"
+    steps:
+      - checkout
+      - print-env-info
+      - restore-npm-cache
+      - run:
+          name: Install dependencies
+          command: npm ci
+  print-env-info:
+    description: "Print build & environment information"
+    steps:
+      - run:
+          name: NPM and NodeJS Version Information
+          command: npm version
+      - run:
+          name: OS Information
+          command: uname -a
+      - run:
+          name: Git and Build Metadata
+          command: |
+            echo $CIRCLE_COMPARE_URL | cut -d/ -f7
+            echo "Git branch: $CIRCLE_BRANCH"
+            echo "Git commit: $CIRCLE_SHA1"
+            echo "Job: $CIRCLE_JOB"
+            echo "Build: $CIRCLE_BUILD_NUM"
+  restore-npm-cache:
+    steps:
+      - restore_cache:
+          keys:
+            - v1-npm-cache--{{ arch }}-{{ .Branch }}-{{ checksum "package-lock.json" }}
+            - v1-npm-cache--{{ arch }}-{{ .Branch }}
+            - v1-npm-cache--{{ arch }}
+  save-npm-cache:
+    steps:
+      - save_cache:
+          key: v1-npm-cache--{{ arch }}-{{ .Branch }}-{{ checksum "package-lock.json" }}
+          paths:
+            - node_modules
+  test:
+    steps:
+      - run:
+          name: Lint
+          command: npm run lint
+      - run:
+          name: Run tests with coverage
+          command: npm run test:cov
+
+jobs:
+  nodejs-v8:
+    docker:
+      - image: node:8
+    steps:
+      - pre-process
+      - test
+      - build
+      - post-process
+  nodejs-v10:
+    docker:
+      - image: node:10
+    steps:
+      - pre-process
+      - test
+      - build
+      - post-process
+  nodejs-latest:
+    docker:
+      - image: node:latest
+    steps:
+      - pre-process
+      - test
+      - build
+      - post-process
+
+orbs:
+  codecov: codecov/codecov@1.0.1
+
+workflows:
+  version: 2.1
+  build-multi-version:
+    jobs:
+      - nodejs-v8
+      - nodejs-v10
+      - nodejs-latest

content/blog/.gitkeep

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+A stub to prevent the "gatsby-source-filesystem" plugin to error on CI builds when this folder doesn't exist.

content/docs/.gitkeep

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+A stub to prevent the "gatsby-source-filesystem" plugin to error on CI builds when this folder doesn't exist.

src/assets/images/.gitkeep

@@ -0,0 +1 @@
+A stub to prevent the "gatsby-source-filesystem" plugin to error on CI builds when this folder doesn't exist.