Add CHANGELOG and CONTRIBUTING

Description

Adds a CHANGELOG.md and CONTRIBUTING.md to help others help us help you.

Resolves #259 (closed)

Changes

N/A. Ironically.

Additions

• A CHANGELOG.md
• A CONTRIBUTING.md
• A new Gradle task checkstyleAll for quickly checking style adherance, to avoid having to run the entire test suite.

Test and Review

To be filled in by the reviewers

• There are no unnecessary files present in the MR

• The continuous integration has no problems with the MR

• The MR is filled in as requested (including labels, milestones, and reviewers)

• The documentation is up-to-date