Split up the about page

[jyn514]

User visible changes

• Split /about into several pages so it's not as long
• Link to /about/builds if a build fails
• Don't suggest opening an issue if the rust compiler isn't recent enough. This is no longer a major issue since we automatically update on each build.
• Add 'Detecting docs.rs from {build.rs,#[cfg]}' sections
• Add 'Missing dependencies' section. Previously this was only linked when opening a new issue.
• Link to the queue from /about and /about/builds
• Note that crates are never allowed internet access, with no exceptions

Internal changes

• Don't rerun the build script whenever a template changes
• Allow dynamically choosing a template in impl_webpage

Addresses #923, #888.

[Nemo157]

I love the centered TOML, we should keep that in the final styling 😁

One suggestion: put a breadcrumb back to the main "About" page in the header of each page:

About | Badges

[jyn514]

Updated!

[jyn514]

@Shnatsel what do you think?

This is /about/builds: https://user-images.githubusercontent.com/23638587/89107717-f55fb480-d400-11ea-962f-c3b94d975607.png

[Shnatsel]

"How you can configure a build" is something I'd click if I was having trouble with my package building. Perhaps make it link to builds page?

Other than that LGTM. Thanks!

[jyn514]

'How you can configure a build' is a different section - it's about [package.metadata.docs.rs] in Cargo.toml, while 'Builds' is more of an overview of how builds work. It's a good idea to link there from a failed build though, I'll do that.

[jyn514]

I also changed the header bar so /about is easier to find.

Before:

After:

[jyn514]

I tried adding icons as well but it didn't come out too well. Not sure why icons are so close to the text, and also some of the tabs it was hard to think of an image that matched.

[jyn514]

Ooh, fa-road looks pretty nice :)

[jyn514]

This is ready for re-review :)

[Kixiron]

Looks good after nits, thanks!