Update documentation

[MicheleCeresoli]

• [x] Remove Utils from the roadmap.
• [ ] Add documentation for loading EOP data.
• [ ] Add light-time transformation tutorial
• [ ] Add tutorial for IERS routines
• [x] Separate use case examples from tutorials
• [ ] Fix HiFi Earth-Moon example with the new EOP interface
• [ ] Fix some documentation typos
• [ ] Add multi-threading tutorial
• [ ] Add Autodiff tutorial