Add Dependency Map, Update Assembly Crawler

[Untested] Assembly Crawler will now accept constructors matching: new(), new(CommandService), new(IDependencyMap).

Add IDependencyMap

Add DependencyMap

src/Discord.Net.Commands/Dependencies/DependencyMap.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+
+namespace Discord.Commands
+{
+    public class DependencyMap : IDependencyMap
+    {
+        private Dictionary<Type, object> map;
+
+        public T Get<T>() where T : class
+        {
+            var t = typeof(T);
+            if (!map.ContainsKey(t))
+                throw new KeyNotFoundException($"The dependency map does not contain \"{t.FullName}\"");
+            return map[t] as T;
+        }
+
+        public void Add<T>(T obj)
+        {
+            var t = typeof(T);
+            if (map.ContainsKey(t))
+                throw new InvalidOperationException($"The dependency map already contains \"{t.FullName}\"");
+            map.Add(t, obj);
+        }
+    }
+}

src/Discord.Net.Commands/Dependencies/IDependencyMap.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Discord.Commands
+{
+    public interface IDependencyMap
+    {
+        T Get<T>() where T : class;
+        void Add<T>(T obj);
+    }
+}