exposing KabamKernel constructor and composing kernel 

@valmy check this out. 
You should be able to create kernel instances like this:
```javascript
var KabamKernel = require('kabam-kernel').KabamKernel;
var kernel = new KabamKernel();
kernel.usePlugin(...);
kernel.usePlugin(...);
kernel.usePlugin(...);
kernel.compose();
```
and then you would have a clean kernel object with only the plugins you've included.