Add Option To Add Custom Header Tags

[mia1024]

I was looking for a way to add a few meta tags into my documentation, but the only solution seems to be writing my own theme and extend on top of alabaster. I know there are options to add <link rel="canonical"> and Google analytics. They are great, but I think it would make the theme more versatile if there is an option to insert a snippet of code into every single generated HTML file.