Now Available on Maven Central

[dmulloy2]

Just a heads up that moving forward, Maven Central will be the preferred repository for ProtocolLib. I copied over 5.1.0, 5.3.0, and 5.4.0. Let me know if there is a need for older versions.

This involves 2 main changes for developers:

• The groupId is now net.dmulloy2 instead of com.comphenix.protocol. This is due to the namespace validation requirements imposed by Maven Central
• repo.dmulloy2.net is deprecated and should be removed. For gradle, add mavenCentral(). For maven, central is included automatically