remove crosspost links from the bottom of list

The crosspost links are already on the top of the article, we do not
need them also on the bottom.

Fixes #87
fix bottom-border on post header

The post header needs to stand out from any h1 inside the post's content
sections
add a line to help with the continue reading link

It's hard to know where to continue reading if the blog post doesn't
quite make it all the way to the bottom of the screen.
throw an exception when template fails to render

If the templates are bad, we should stop building. Building a website
with a bunch of error messages is pretty pointless...

Fixes #85
fix exception in test template

So how long has this been an issue I wonder...
add test to check default theme syntax

Found a lot of horrible design choices in this test, and even revealed a
bug in the template! Excellent idea this.

We need to do more purturbation of the variables, add/remove navs,
links, and otherwise, in order to get a good coverage of the themes.

Fixes #86
fix default layout error if no main nav

All navs should be optional. This was revealed by the new theme check
test. Yay!
release v0.015