Extraction: initial import

Extract Radix Tree implementation from `Beryl` project into an
standalone library to facilitate usage by other developers.

- Move `Tree`, `Node` and `Result` into `Radix` namespace
- Clenaup standalone README and describe usage

spec/radix/result_spec.cr

@@ -0,0 +1,67 @@
+require "../spec_helper"
+
+module Radix
+  describe Result do
+    describe "#found?" do
+      context "a new instance" do
+        it "returns false when no payload is associated" do
+          result = Result.new
+          result.found?.should be_false
+        end
+      end
+
+      context "with a payload" do
+        it "returns true" do
+          node = Node.new("/", :root)
+          result = Result.new
+          result.use node
+
+          result.found?.should be_true
+        end
+      end
+    end
+
+    describe "#key" do
+      context "a new instance" do
+        it "returns an empty key" do
+          result = Result.new
+          result.key.should eq("")
+        end
+      end
+
+      context "given one used node" do
+        it "returns the node key" do
+          node = Node.new("/", :root)
+          result = Result.new
+          result.use node
+
+          result.key.should eq("/")
+        end
+      end
+
+      context "using multiple nodes" do
+        it "combines the node keys" do
+          node1 = Node.new("/", :root)
+          node2 = Node.new("about", :about)
+          result = Result.new
+          result.use node1
+          result.use node2
+
+          result.key.should eq("/about")
+        end
+      end
+    end
+
+    describe "#use" do
+      it "uses the node payload" do
+        node = Node.new("/", :root)
+        result = Result.new
+        result.payload?.should be_falsey
+
+        result.use node
+        result.payload?.should be_truthy
+        result.payload.should eq(node.payload)
+      end
+    end
+  end
+end