Improve selection coloring + add find highlight support.

Hi Michael,

I thought I'd contribute back a minor update to your Railscasts.tmTheme. Gets rid of the out-of-place bluish highlight color and adds support for find highlighting.

![Screen Shot 2013-02-12 at 10 20 49 PM](https://f.cloud.github.com/assets/347072/151684/b5d27d14-758c-11e2-92bf-0789a65c8f2d.jpg)

Thanks for the superb project! Definitely helping round-out my skills.