Optimizer interface and sample implementation (#19)

Reviewed-on: Rubydragon/MetagraphOptimization.jl#19
Co-authored-by: Anton Reinhard <anton.reinhard@proton.me>
Co-committed-by: Anton Reinhard <anton.reinhard@proton.me>

src/MetagraphOptimization.jl

@@ -31,8 +31,10 @@ export children
 export compute
 export data
 export compute_effort
+export task
 export get_properties
 export get_exit_node
+export operation_stack_length
 export is_valid, is_scheduled
 
 # graph operation related
@@ -68,6 +70,11 @@ export get_compute_function
 export cost_type, graph_cost, operation_effect
 export GlobalMetricEstimator, CDCost
 
+# optimization
+export AbstractOptimizer, GreedyOptimizer, ReductionOptimizer, RandomWalkOptimizer
+export optimize_step!, optimize!
+export fixpoint_reached, optimize_to_fixpoint!
+
 # machine info
 export Machine
 export get_machine_info
@@ -117,6 +124,7 @@ include("node/properties.jl")
 include("node/validate.jl")
 
 include("operation/utility.jl")
+include("operation/iterate.jl")
 include("operation/apply.jl")
 include("operation/clean.jl")
 include("operation/find.jl")
@@ -136,6 +144,11 @@ include("task/properties.jl")
 include("estimator/interface.jl")
 include("estimator/global_metric.jl")
 
+include("optimization/interface.jl")
+include("optimization/greedy.jl")
+include("optimization/random_walk.jl")
+include("optimization/reduce.jl")
+
 include("models/interface.jl")
 include("models/print.jl")