Code cleanup and begin using Travis CI

Hi Blake,

Thought I'd give you a pull request.

The DESCRIPTION cleanup is pretty straightforward, just removing some automatically generated fields.

I've added Travis CI which you should find to be beneficial. You'll need to enable that, which can be done via the docs on [Travis CI](http://docs.travis-ci.com/user/getting-started/).

I've also made a start on some package checker fixes. There are still a few issues remaining, most of which are documentation-related. However there are some which are code-related and should be fixed, e.g.:

```
direction_plot: no visible binding for global variable ‘direction’
```

This suggests you're missing a variable "direction" that should be an argument to the function rather than assumed to be in some environment. If it is supposed to be in an environment, you'll need to explicitly pull it out of the environment (via `get` or something like that).