Add isbn-core (akullpp#1103)

README.md

@@ -688,6 +688,7 @@ _Everything else._
 - [FF4J](https://github.com/ff4j/ff4j) - Feature Flags for Java.
 - [FizzBuzz Enterprise Edition](https://github.com/EnterpriseQualityCoding/FizzBuzzEnterpriseEdition) - No-nonsense implementation of FizzBuzz made by serious businessmen for serious business purposes. (No explicit license)
 - [IP2Location.io Java SDK](https://github.com/ip2location/ip2location-io-java) - Wrapper for the IP2Location.io Geolocation API and the IP2WHOIS domain WHOIS API.
+- [ISBN core](https://github.com/ladutsko/isbn-core) - A small library that contains a representation object of ISBN-10 and ISBN-13 and tools to parse, validate and format one.
 - [J2ObjC](https://github.com/google/j2objc) - Java-to-Objective-C translator for porting Android libraries to iOS.
 - [JBake](https://jbake.org) - Static website generator.
 - [JBot](https://github.com/rampatra/jbot) - Framework for building chatbots. (GPL-3.0-only)