favicon feature

Hello. I like syte and I added to my syte support to favicons.

I thought that it could be a nice idea to divide the code in modules and I decided to create an independent file for this.

Also I think that this feature is nice for others aspects of the blog. The idea is to isolate some code sections, for example SEO, Twitter Cards and others for easy access and modification and adapted for each user.

What's your opinion?

Maybe is a stupid (and newbie) pull request but I decided to share it.

Regards ;)