Use mysql_config to find the location of Mysql's headers and libraries directories

Let me preface this with, I'm no expert in building C libs cross platform, but I had an issue building this on OSX.

So I replaced the list of directories to search for headers and libraries with the `mysql_config` command that returns the exact location of them. I've only tested this on OSX and Linux (Ubuntu), as I don't have access to any other Unix or Windows systems.