StringBuffer -> StringBuilder and other modernizations

[GlenKPeterson]

Thank you for adding a Maven project to https://github.com/djmdjm/jBCrypt

BCrypt needs to be efficient because it relies on "work" for security. If someone else can make a faster version, they can break your encryption more cheaply than you can make it. StringBuilder is a more efficient replacement for StringBuffer, so I wanted to make that change.

Using supported software is considered more secure than unsupported, so I moved us up to Java 8.

Added the Maven Enforcer plugin to make checking versions easier in the future.

Upgraded to the latest JUnit.

Added CHANGELOG.md and .gitignore files.

Basically I wanted to update things as securely as possible while changing as little as possible. What do you think?

[v4ultboy]

I ended up using Password4j which is frequently maintained.