Switched to classmap

[nrbrook]

I have switched to classmap by changing the composer.json file and removing the now unnecessary requires in Mixpanel.php. I think this works...needs some testing. This was in response to #8

[jbwyme]

Thanks for the pull request. My main concern is that I want people who are using php < 5.3 to be able to use this library. Correct me if I'm wrong, but I believe that by switching to classmap it will require namespacing

[nrbrook]

Composer requires php >5.3.2 so it doesn't matter. Just leave in the requires if you want it to be compatible with php < 5.3.

[nrbrook]

Classmap is used to auto load libraries that do not comply with psr-0, so you don't need to use namespaces. As you can see in my pull request it doesn't add namespaces.

[jbwyme]

Oh ok great I'll do some testing with it and see about getting it merged. Thanks!