Create stub for request_parse_body()

[Girgias]

@iluuu1994 I created a stub, if you could document this. :)

[iluuu1994]

Thank you Gina! Can you review this? (Can't add you as a reviewer since you created the PR).

[Girgias]

Some comments, the main one being the indentation :)

[iluuu1994]

Thank you @Girgias! Hopefully it looks good now.

[Girgias]

See the last review comments, as exceptions should be described in a dedicated error section.

If you are happy with the wording, feel free to commit and merge :)

[iluuu1994]

Thank you!