Fix lib.rs link format

[antonio-sc66]

Fix wrong links format.

Currently, when performing: cargo doc, the next warnings are raised:

warning: this URL is not a hyperlink
   --> src/lib.rs:322:35
    |
322 | /// V1 maximum size is 263 bytes: https://mavlink.io/en/guide/serialization.html
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use an automatic link instead: `<https://mavlink.io/en/guide/serialization.html>`
    |
    = note: bare URLs are not automatically turned into clickable links
    = note: `#[warn(rustdoc::bare_urls)]` on by default

warning: this URL is not a hyperlink
   --> src/lib.rs:508:35
    |
508 | /// V2 maximum size is 280 bytes: https://mavlink.io/en/guide/serialization.html
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use an automatic link instead: `<https://mavlink.io/en/guide/serialization.html>`
    |
    = note: bare URLs are not automatically turned into clickable links

[patrickelectric]

@antonio-sc66 can you squash the commits ?

[antonio-sc66]

It's squashed now

[patrickelectric]

Thanks!