Improve mobile layout

[noelleleigh]

This PR makes the following changes in an effort to improve the legibility of the navigation links in narrow screen sizes:

• The <h2> and <ul> pairs in src/inc/meta.nav.htm are now enclosed in <section>s in order to more easily style them as a single unit.
• Added more media query screen width divisions combined with the :nth-child() pseudo-class in order to simulate a flexbox wrapping layout and to prevent floated <sections> from getting caught on each other in visually unpleasant ways.

I tested it in the latest versions of Chrome, Firefox, NetSurf, and Internet Explorer and they all seem to render these changes alright from what I can tell. I'm happy to make changes if requested.

Note: This PR doesn't include the changes produced by running the src/build.sh script because of how many changed files it produced that cluttered up the diff.

[neauoire]

Damn, your made the PR the moment I pushed a kind of fix for this, I enclosed the nav in a <details> element so people on mobile can collapse it.

[noelleleigh]

Damn, your made the PR the moment I pushed a kind of fix for this, I enclosed the nav in a <details> element so people on mobile can collapse it.

Would you like me to incorporate my changes with your fix?

[noelleleigh]

I've integrated my changes into the <details>.

[neauoire]

Yes! Sorry I was asleep, thanks for the patch Noelle <3

[noelleleigh]

You’re welcome! Don’t forget to run build.sh to apply the changes!