Add .npmignore

This package is much larger than it needs to be on npm.

Original:

```
~/g/f/fluxxor ((1.4.1)|…) $ npm pack
fluxxor-1.4.1.tgz
~/g/f/fluxxor ((1.4.1)|…) $ wc -c fluxxor-1.4.1.tgz
 3477805 fluxxor-1.4.1.tgz
```

With the `.npmignore` from this patch:

```
~/g/f/fluxxor (npmignore|…) $ wc -c fluxxor-1.4.1.tgz
   12854 fluxxor-1.4.1.tgz
```