What is the purpose of the change

Upgrade to 4.0.0

Brief ChangeLog

1. Upgrade the minimum supported JDK version to 8.
2. Remove Rough Recorder mode and use Accurate Recorder mode as the default.
3. Introduce FastAtomicIntArray for extremely high-throughput methods.
4. Use long[] as the underlying data structure for AtomicIntHashCounter.
5. Code cleanup.

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a GITHUB_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Format the pull request title like [MyPerf4J-XXX] Fix NullPointerException when host is null #XXX. Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist.
• Run mvn clean package -Dmaven.test.skip=false to make sure unit-test pass.