`const fn` is no longer coming soon (const keyword docs)
The `const` keyword [documentation](https://doc.rust-lang.org/std/keyword.const.html) mentions that `const fn`s are coming soon, but they have already been added.
Most of these will eventually be filled, but right now travis-ci enjoys
complaining about the fact that there's links that lead nowhere, so
they're gone. Hopefully someone remembers to re-add them later.
This commit also splits out linky-line-thingies into two lines, which
judging from the source code for tidy, should be enough to make it shut
up and accept me for who I am, dammit.
I think it might be used in some other things, but I'm not fluent enough
at sifting through the rust compiler's source code to find every use of
a specific keyword.
This leaves the question of how to document the `extern` keyword, what
with how much overlap it has with `crate`, but that's used with ABI
stuff so that should be fine.
Turns out writing docs on keywords that are used in multiple different
places in entirely different contexts gets a little harder. I put a
footnote on `*const` syntax just to make sure you can find it if need
be, but it might need more detail.
The whole keyword docs thing is pretty new in Rust's history and needs
some work before it's a shining gem. Here's hoping I can provide that.
I basically shoved in a bunch of the most important information from the
reference and the book, along with leaving links to both at the end. I
don't think keyword docs need to have complete detail, just all the
broad strokes, so if someone's confused about a usage of a keyword they
can look at the std documentation for that keyword.
