Add code for custom JS

Add liquid templating in footer to allow pages to specify their own JS
files to load. Also generalize the bit of styling I was using for padding
the left side of most pages
Fix build error

Fix liquid templating that caused 1d575fb to fail to build the static
site on GitHub.

Also use jQuery to autohide/toggle visibility of list of posts on tag
page
Tweak sidebar js

Tweak the jQuery that toggles sidebar archive visibility so that it only
applies on click of the actual link and not the whole <li> element