v1.0.3 Better Tests and @NotNull annotations

Mainly proper and readable tests using the given, when, then template and assertJ assertions. Also NotNull annotations for public methods and their arguments, mainly with Kotlin consumers in mind.

What's Changed

• Proper-er unit tests, bit of javadoc and annotations by @Abductcows in #10
• remove test println statements by @Abductcows in #11
• increment version by @Abductcows in #12

Full Changelog: v1.0.2...v1.0.3