During the last coding sprint,@cgalelli and I tried to implement a generalised 1D model to

1. Avoid code duplication between temporal and spectral models
2. Enable an easy API for fitting other parameters, eg, phase, frequency, etc

I have an example notebook here:https://github.com/AtreyeeS/test_notebooks/blob/master/general_model.ipynb
(there is some ugly jugglery in the integral function, but there should be more elegant solutions with bumpy)

I think this works, and we might consider implementing it for 2.0