Add links to types in documentation

[CryZe]

Rust 1.48 just came out with a proper built-in way to mention types in documentation that you can click on and get linked to that specific type. Before you needed to write the relative URL of the type which was both cumbersome and based on an implementation detail, so we just never linked to any types. Here's the blog post:

Rust 1.48

[Eein]

I've started a little work on this. I've attempted to avoid changing as much of the wording as possible for now; however I feel like some things are looking to busy now: See:

The rules i've been following is to only link to things when they're describing another module; if they are describing themselves I simply backticked them to still display them as formatted text.

I suppose a simple wording change for things describing themselves may help a bit:

For example:

timing - The timing module provides everything necessary for working with times and measuring them.
TimeSpan - A TimeSpan represents a certain span of time.

could be:

timing - Provides functions for working with times and measuring them.
TimeSpan - Represents a specific span of time.

I can likely expand on the documentation later in a different unit of work once the initial types are done; following the recommendations by: https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html#documenting-components

For example, if you include a blank line between the first and second paragraphs, it will only return the first sentence to summarize and allow you to add detail when you click through to the actual Struct/Enum/etc

[CryZe]

Yeah that sounds fine.