Update Font Awesome & Tera and refactor templates

[Kixiron]

• Update to Font Awesome 5
• Update to Tera 1.5
• Use custom filters for making icons
• Made some of the icons fancier

Before:

After:

r? @pietroalbini

[Nemo157]

Can we make the icons in the file list fixed width?

[pietroalbini]

Could you also squash away all the previous commits? We don't need to have fontawesome vendored forever inside the repository even though we don't use it.

[jyn514]

Can we separate the upgrade from the refactor? I think I heard the refactor depends on the upgrade, so we could do the upgrade first without any large changes to docs.rs itself.

[Kixiron]

The upgrade is just bumping versions, does that matter?

[jyn514]

Yes, not all projects correctly follow semver (or make accidental breaking changes) and even if there's no breaking change there could be a large performance difference, since most projects don't track that. For example this happened with tokio 0.2 and html5ever 0.24.

[Nemo157]

Where does this URL come from? I don't see anywhere on the main website listing it as a CDN?

[Kixiron]

This page in the codeblock of the Upgrading Manually section

[jyn514]

Can we separate the upgrade from the refactor? I think I heard the refactor depends on the upgrade, so we could do the upgrade first without any large changes to docs.rs itself.

We discussed this on discord and decided that since there have been very few changes since 1.3.1 it's ok to do both at once.