fixing issue#99, added API and removed EventLoopGroup in README

[JeffZhou215]

Added MySQLConnection under Tests/Utilities.swift; updated the README.md.

[MahdiBM]

Thanks for the pull request and for taking the time.

Before letting you down, I want to share that my first PR, even though it was a large effort, was rejected by @0xTim and @jdmcd because it wouldn't fit (vapor/queues#98).

Your changes are fine but they don't address the main issue, so we can't take this PR as it stands.
For example you haven't changed any of the public functions to work without accepting an EventLoop.
Adding that functions to tests doesn't help at all because that can only be used as an internal testing helper (which is unneeded) and users won't be able to take advantage of it.

If you really want to give it another try, you can take some help from this other similar PR which addressed the same problem in a similar repository: vapor/postgres-nio#389

[JeffZhou215]

Thanks @MahdiBM! I will definitely spend more time on this. I truly appreciate your feedback about this issue and will take a look of the similar issue to make a new pr soon.