Changes as of Saturday

* Finally moved the `aspect` folder one level up, to get rid of the `PYAS-core` level
* New utility (`evaluate`) to quickly evaluate FITS files on the SBC (rather than downloading them first).  See the documentation in `evaluate.cpp`
* Now handles the termination signal too, so will clean up normally upon `systemd` requests to `stop` or `restart`
* Protected against an edge case where two saving threads could be started at exactly the same time

Merging immediately