Document all the variables

docs/src/sequence_optimisation.md

src/components/abstract_types.jl

src/components/pulses/sinc_pulses.jl

src/components/readouts/ADCs.jl

src/containers/building_blocks.jl

src/parts/spoilt_slice_selects.jl

src/parts/trapezoids.jl

src/sequences/diffusion_spin_echoes.jl

src/sequences/spin_echoes.jl

src/variables.jl