Create short permalinks for sections and crates

[nicoburns]

It is currently possible to link directly to a section of blessed.rs using a link like https://blessed.rs/crates#section-graphics-subsection-gui, which works however:

• The links are long an unwieldy
• The links are tied to the section name which is liable to change

We should add "short links" like https://blessed.rs/crates#gui which are snappy and can also be preserved if/when the crates list is reorganised. We could also add crate specific links like https://blessed.rs/crates#axum or similar.