Minor tweaks

Hey, I did some small formatting updates to the readme and updated the .npmignore.

The only remaining things I might think would be useful in the readme would be:

* An example of `registerSelector`.
* A note on what the default values are for all the options passed to `configure`.
* An explanation of what the differences are between `src/nwmatcher-base.js`, `src/nwmatcher-noqsa.js` (that one is easy to figure out), and `src/nwmatcher.js`.

Hope this helps, and sorry for taking so long to get around to this!