Update version number and changelog for 0.21 #105

	name: Gradle Build

	on: [push, pull_request]

	jobs:
	build:
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v4
	- name: Set up JDK 13
	uses: actions/setup-java@v3
	with:
	java-version: '13'
	distribution: 'adopt'
	- name: Validate Gradle wrapper
	uses: gradle/wrapper-validation-action@56b90f209b02bf6d1deae490e9ef18b21a389cd4
	- name: Cache Gradle packages
	uses: actions/cache@v3
	with:
	path: \|
	~/.gradle/caches
	~/.gradle/wrapper
	key: ${{ runner.os }}-gradle-${{ hashFiles('*/.gradle', '*/gradle-wrapper.properties') }}
	restore-keys: \|
	${{ runner.os }}-gradle-
	- name: Build with Gradle
	run: ./gradlew build
	- name: Check code formatting
	run: ./gradlew spotlessCheck
	- name: Cleanup Gradle Cache
	# Remove some files from the Gradle cache, so they aren't cached by GitHub Actions.
	# Restoring these files from a GitHub Actions cache might cause problems for future builds.
	run: \|
	rm -f ~/.gradle/caches/modules-2/modules-2.lock
	rm -f ~/.gradle/caches/modules-2/gc.properties

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