Allow easier local customisation

[willthames]

Allow nav bar to be generated from custom/navigation (as default theme) Change feedburner to use bespoke feedburner settings

• site.feedburner_url - feedburner url for feed
• site.feedburner_img_url - image for feedcount Made subscribe buttons hide if no value set Sidebar can be on left or right. index.html includes sidebar.html for reuse

I'd rather remove _includes/custom/navigation.html from the repo entirely but I guess it's nice to have a default This will break your pages until you add feedburner_url and feedburner_img_url to your _config.yml

[barmstrong]

Awesome work! Thanks for contributing this and sorry it took so long for me to see it (email must have flown past my inbox). Cheers.