Merge branch 'development_0.9.3/2.2.1' of gitlab.eps.surrey.ac.uk:ri0005/binary_c-python into development_0.9.3/2.2.1

fixed issues with grid spacings

new gridtype: "discrete". This samples the grid points and does not set the probability.

add a fix to distinguish between centred and edge grids when computing number of points over which we should loop and phasevols

also added a warning in the const_dt spacing function to catch the edge case where tmax or max_evolution_time are shorter than the first timestep, which would lead to an empty interpolation table

Merge branch 'development_0.9.2/2.2.1' of gitlab.eps.surrey.ac.uk:ri0005/binary_c-python into development_0.9.2/2.2.1