Better document new gradients

src/gradients/gradients.jl

 """
 Module defining sub-types of the [`GradientBlock`](@ref), i.e., any [`BuildingBlock`](@ref) that only defines a gradient profile.
 
-In principle, there are only three types of [`GradientBlock`]:
+There are only three types of [`GradientBlock`] objects:
 - [`ChangingGradientBlock`](@ref): any gradient changing linearly in strength.
 - [`ConstantGradientBlock`](@ref): any gradient staying constant in strength. These can overlap with a pulse (`SliceSelectPulse`).
 - [`InstantGradientBlock`](@ref): an infinitely short gradient pulse.
 
-All other gradient profiles are made up of [`ChangingGradientBlock`](@ref) and [`ConstantGradientBlock`](@ref) and hence are technically sequences.
-They are still included here for clarity:
-- [`PulsedGradient`](@ref)
-- [`GradientWaveform`](@ref)
+Combinations of these should sub-type from [`SpecificWaveform`](@ref).
 """
 module Gradients
 
@@ -19,7 +16,7 @@ include("instant_gradients.jl")
 
 
 import ..BuildingBlocks: GradientBlock
-import .ChangingGradientBlocks: ChangingGradientBlock
+import .ChangingGradientBlocks: ChangingGradientBlock, split_gradient
 import .ConstantGradientBlocks: ConstantGradientBlock
 import .InstantGradients: InstantGradientBlock
 end
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