Add public initializers to SimpleNode, SimpleEdge and SimpleGraph

Author: nmandica

Sources/Graph/SimpleEdge.swift

@@ -2,4 +2,10 @@ public struct SimpleEdge: Edge {
     public var source: String
     public var target: String
     public var value: Int
+    
+    public init(source: String, target: String, value: Int) {
+        self.source = source
+        self.target = target
+        self.value = value
+    }
 }

Sources/Graph/SimpleGraph.swift

@@ -3,6 +3,11 @@ import Foundation
 public struct SimpleGraph: Graph {
     public var nodes: [SimpleNode]
     public var edges: [SimpleEdge]
+    
+    public init(nodes: [SimpleNode], edges: [SimpleEdge]) {
+        self.nodes = nodes
+        self.edges = edges
+    }
 }
 
 extension SimpleGraph {

Sources/Graph/SimpleNode.swift

@@ -1,4 +1,9 @@
 public struct SimpleNode: Node {
     public var id: String
     public var group: Int
+    
+    public init(id: String, group: Int) {
+        self.id = id
+        self.group = group
+    }
 }