Provide better way to write analyses and transformations

ast/arrays.py

ast/assign.py

ast/ast_node.py

ast/bin_op.py

ast/block.py

ast/branches.py

ast/cast.py

ast/loops.py

ast/math.py

ast/memory.py

ast/mutator.py

ast/select.py

ast/visitor.py

sim/particle_simulation.py

sim/timestep.py

sim/vtk.py

transformations/flatten.py

transformations/simplify.py