Set up custom domain name

The CNAME file was added so that my domain name will point to this
github page. Once DNS records have propagated (~24 hours max), then the
custom 404 page should work.
Fix non-post pages title

The 'About' and 'Projects' pages were using the post layout, causing the
post header to show up above their titles. This was fixed by changing
the layout to default.
Add post header

Fixed #2 by using code of rbirnie in his _includes/posts/post.html