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>

docs/src/lib/internals/estimator.md

@@ -1,4 +1,4 @@
-# Models
+# Estimation
 
 ## Interface
 

docs/src/lib/internals/optimization.md

@@ -0,0 +1,41 @@
+# Optimization
+
+## Interface
+
+The interface that has to be implemented for an optimization algorithm.
+
+```@autodocs
+Modules = [MetagraphOptimization]
+Pages = ["optimization/interafce.jl"]
+Order = [:type, :constant, :function]
+```
+
+## Random Walk Optimizer
+
+Implementation of a random walk algorithm.
+
+```@autodocs
+Modules = [MetagraphOptimization]
+Pages = ["estimator/random_walk.jl"]
+Order = [:type, :function]
+```
+
+## Reduction Optimizer
+
+Implementation of a an optimizer that reduces as far as possible.
+
+```@autodocs
+Modules = [MetagraphOptimization]
+Pages = ["estimator/reduce.jl"]
+Order = [:type, :function]
+```
+
+## Greedy Optimizer
+
+Implementation of a greedy optimization algorithm.
+
+```@autodocs
+Modules = [MetagraphOptimization]
+Pages = ["estimator/greedy.jl"]
+Order = [:type, :function]
+```