First attempt at adding category navigation

This is super WIP. There's a lot of issues that need to be addressed with this design, notably the screen space utilisation on mobile devices and the repetition of content and functionality on the homepage.
Improved how the category navigation bar handles resizing

It looks much better on mobiles although it still takes up way too much space. I suspect this will only be fixable with a hamburger menu
The current page's category is now highlighted in the category bar
Updated category generation plugin so that category pages are assigned their own category
Fixed teeny tiny spacing issues in the category bar

So inline-blocks are affected by white space. As a result, this liquid monstrosity was born. I hope I never need to modify this.
Category background colour is now edge to edge on mobile screens
Minor SASS cleanup
Added transitions highlight effect in category bar
Added hamburger button on small screens

It isn't properly aligned vertically. Will fix.
First implementation of hamburger menu

Untested, probably doesn't work in IE, etc., etc.
Added transitions to site header's hamburger menu

It uses a max-width hack to get the animations working and they don't look quite right but it's the best that can be done ATM.
Concatenated multipage scripts into a single file
Integrated categories menu into the home page menu

The categories menu replaces the homepage menu but is functionally
identical. On mobile devices/small screens, the categories menu will be
automatically expanded on the homepage.
Menu instructions now disappear after first use
Inverted hamburger button media queries
Specified property to animate in hamburger menu
Cleaned up homepage's SASS
Merge branch 'category-navigation'