Added error template, added blog title to title tag.

Hi Dale,

Thank you for your work on Uno, it's a real beauty!

I made some small modifications to the theme which I thought you may like.

- Added an error template for 404 errors etc.
- Added the blog title to the `<title>` tag. 

Homepage: `Blog Title`
Post pages: `Post Title - Blog Title`
Error pages: `Error Title - Blog Title`
Tag pages: `Tag Name - Blog Title`