Adding changelog for the changes

1. 2D cell locators
2. Particle advection module statuses

docs/changelog/cell_locator_changes.md

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+# Updating structured cell locators
+
+VTK-m will mow allow locating containing cells for a point using `CellLocatorUniformGrid`
+and `CellLocatorRectilinearGrid` for 2D grids.
+
+Users are required to create the locator objects as they normally would.
+However, the `FindCell` method in `vtkm::exec::CellLocator` still requires users
+to pass a 3D point as an input.
+
+Further, the structured grid locators no longer use the `vtkm::exec::WorldToParametricCoordinates`
+method to return parametric coordinates, instead they use fast paths for locating
+points in a cell of an axis-aligned grid.
+
+Another change for the `CellLocatorRectilinearGrid` is that now it uses binary search
+on individual component arrays to search for a point.

docs/changelog/particle_status_changes.md

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+# Updating particle status for advection
+
+There are now special statuses for Particle, Integrator, and Evaluator.
+
+The particle advection modules only supported statuses for particles and made it
+difficult to handle advanced integtator statuses.
+Now each of the three important modules return their own statuses
+
+Particles have `vtkm::worklet::particleadvection::ParticleStatus`,
+Integrators have `vtkm::worklet::particleadvection::IntegratorStatus`, and
+Evaluators have `vtkm::worklet::particleadvection::EvaluatorStatus`.
+
+Further, names of the statuses in `vtkm::worklet::particleadvection::ParticleStatus`
+have changed
+
+`ParticleStatus::STATUS_OK` is now `ParticleStatus::SUCCESS`, and there is another
+status `ParticleStatus::TOOK_ANY_STEPS` which is active if the particle has taken
+at least one step with the current data.
+
+There are few more changes that allow particle advection in 2D structured grids.