Allow tsl8 callback to only require modules (callback.length === 1)

Hey this is actually several small tweaks, all wrapped together.

The goal was to be able to just do 
```js
require('tesselate')(['accel-mma84'],function(m) {
  m.accel.on('data', function(data) { console.log(data) });
});
```
Instead of forcing the passing of the tessel module.