Issue #451: Reorder function sections on website

[athowes]

Description

This PR closes #451. Self explained. Adds issue #457.

The order is now:

reference:
- title: Linelist data
- title: Model fitting
- title: Naive model
- title: Latent model
- title: Postprocess
- title: Diagnostic functions
- title: Assert validity of objects
- title: Family
- title: Formula
- title: Prior distributions
- title: Stan code
- title: Simulation
- title: Data
- title: Reexported functions

Checklist

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• I have added or updated unit tests where necessary.
• I have updated the documentation if required.
• My code follows the established coding standards.
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