CI: switch to GitHub Actions

This commit:
* Adds a GH Actions `cs` workflow for the code style and vardump checks which were previously run on Travis.
    These checks only need to run against one PHP version as the results will be the same independently of the PHP version these checks are run on.
* Adds a GH Actions `test` workflow for the linting and unit test checks which were previously run on Travis.
* Uses the [`cs2pr`](https://github.com/staabm/annotate-pull-request-from-checkstyle) tool to display the results of the PHP linting and the results of the PHP code style check in-line in the file diff in the PR.
* Removes the, now redundant, `.travis.yml` configuration.
* Updates the `.gitattributes` file.
* Updates the "Build Status" badge in the Readme to use the results from the GH Actions runs.

.gitattributes

@@ -2,6 +2,6 @@
 /tests export-ignore
 .gitattributes export-ignore
 .gitignore export-ignore
-.travis.yml export-ignore
+/.github export-ignore
 phpunit.xml.dist export-ignore
 phpcs.xml.dist export-ignore

.github/workflows/cs.yml

@@ -0,0 +1,38 @@
+name: CS
+
+on:
+  push:
+  pull_request:
+  # Allow manually triggering the workflow.
+  workflow_dispatch:
+
+jobs:
+  checkcs:
+    name: 'Check code style'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.4'
+          coverage: none
+          tools: cs2pr
+
+      # Install dependencies and handle caching in one go.
+      # @link https://github.com/marketplace/actions/install-composer-dependencies
+      - name: Install Composer dependencies
+        uses: "ramsey/composer-install@v1"
+
+      - name: Check PHP code style
+        continue-on-error: true
+        run: vendor/bin/phpcs --report-full --report-checkstyle=./checkstyle.xml
+
+      - name: Show PHPCS results in PR
+        run: cs2pr ./checkstyle.xml --graceful-warnings
+
+      - name: Make sure no vardumps remain
+        run: composer vardumpcheck

.github/workflows/test.yml

@@ -0,0 +1,53 @@
+name: Test
+
+on:
+  pull_request:
+  push:
+  # Allow manually triggering the workflow.
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        php: ['5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
+        experimental: [false]
+
+        include:
+          - php: '8.1'
+            experimental: true
+
+    name: "Test on PHP ${{ matrix.php }}"
+    continue-on-error: ${{ matrix.experimental }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: none
+          tools: cs2pr
+
+      # Install dependencies and handle caching in one go.
+      # @link https://github.com/marketplace/actions/install-composer-dependencies
+      - name: Install Composer dependencies - normal
+        if: ${{ matrix.experimental == false }}
+        uses: "ramsey/composer-install@v1"
+
+      # For the PHP "nightly", we need to install with ignore platform reqs as not all dependencies allow it.
+      - name: Install Composer dependencies - with ignore platform
+        if: ${{ matrix.experimental == true }}
+        uses: "ramsey/composer-install@v1"
+        with:
+          composer-options: --ignore-platform-reqs
+
+      - name: Lint
+        run: composer phplint -- --checkstyle | cs2pr
+
+      - name: Run unit tests
+        run: composer phpunit

README.md

@@ -32,5 +32,6 @@ echo $highlighter->getWholeFile($fileContent);
 ------
 
 [![Downloads this Month](https://img.shields.io/packagist/dm/php-parallel-lint/php-console-highlighter.svg)](https://packagist.org/packages/php-parallel-lint/php-console-highlighter)
-[![Build Status](https://travis-ci.org/php-parallel-lint/PHP-Console-Highlighter.svg?branch=master)](https://travis-ci.org/php-parallel-lint/PHP-Console-Highlighter)
+[![CS](https://github.com/php-parallel-lint/PHP-Console-Highlighter/actions/workflows/cs.yml/badge.svg)](https://github.com/php-parallel-lint/PHP-Console-Highlighter/actions/workflows/cs.yml)
+[![Test](https://github.com/php-parallel-lint/PHP-Console-Highlighter/actions/workflows/test.yml/badge.svg)](https://github.com/php-parallel-lint/PHP-Console-Highlighter/actions/workflows/test.yml)
 [![License](https://poser.pugx.org/php-parallel-lint/php-console-highlighter/license.svg)](https://packagist.org/packages/php-parallel-lint/php-console-highlighter)