Use config api as programmatic argument

```js
require('testee').test(config);
```
instead of:
```js
require('testee').test(files, browsers, config);
```

This would make working with the programmatic API much more familiar to using a command line config or Gruntfile.

Start at the programmatic API entry point exposed by require('testee').test and compare how it currently handles files, browsers, and config. Done means the API accepts a config object directly, matching the issue's example, while the existing argument form remains understood if the project expects compatibility.

Written by the indexing model from the issue text.