Configurable GA, Atom RSS feed, and fewer CSS bytes

[ssorallen]

Thanks for the great theme. I wanted an RSS feed and my own Google Analytics settings and added them in this pull request.

• Move Google Analytics settings to _config.yml to let the user configure them. If either setting is missing, the <script> block is not inserted. That allows disabling GA if it's not wanted.
• Add /atom.xml and links to it in the head to provide an RSS feed of the blog.
• Simplify selectors that were using tag selectors when they didn't need to.

[ssorallen]

I can split these into separate pull requests if that's better.

[mx3m]

Great stuff!

• GA settings via _config.yml! Why not.
• RSS feed feels required indeed. Thanks for adding this.

Now for the selectors, I don't know. Can you submit a different pull request for this, if possible? I personally like to have my tag selectors as specific as possible to understand what I'm looking at. Maybe it's a bad habit?

[ssorallen]

I tend to use the least-specific selector that will match the elements I want. It leads to more reusable CSS and makes for easier overriding of styles down the line. That said, it does depend on personal preference; there's not really a wrong way to write CSS if it works.

I will remove the CSS changes out and create a new pull request.

[mx3m]

I know what you mean. For themes, in general, I tend to use specific selectors so it's easier for people to override my basic styles (in this case, I could have used #posts for something else than ul; EDIT: I just realised that what I'm saying doesn't make any sense... nevermind). But again, that might just be an old and bad habit =/

Thank you so much for contributing to this theme! Looking forward to your new pull request!