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/node_spec.cr

@@ -0,0 +1,102 @@
+require "../spec_helper"
+
+module Radix
+  describe Node do
+    describe "#key=" do
+      it "accepts change of key after initialization" do
+        node = Node.new("abc")
+        node.key.should eq("abc")
+
+        node.key = "xyz"
+        node.key.should eq("xyz")
+      end
+    end
+
+    describe "#payload" do
+      it "accepts any form of payload" do
+        node = Node.new("abc", :payload)
+        node.payload?.should be_truthy
+        node.payload.should eq(:payload)
+
+        node = Node.new("abc", 1_000)
+        node.payload?.should be_truthy
+        node.payload.should eq(1_000)
+      end
+
+      it "makes optional to provide a payload" do
+        node = Node.new("abc")
+        node.payload?.should be_falsey
+      end
+    end
+
+    describe "#priority" do
+      it "calculates it based on key size" do
+        node = Node.new("a")
+        node.priority.should eq(1)
+
+        node = Node.new("abc")
+        node.priority.should eq(3)
+      end
+
+      it "returns zero for catch all (globbed) key" do
+        node = Node.new("*filepath")
+        node.priority.should eq(0)
+
+        node = Node.new("/src/*filepath")
+        node.priority.should eq(0)
+      end
+
+      it "returns one for keys with named parameters" do
+        node = Node.new(":query")
+        node.priority.should eq(1)
+
+        node = Node.new("/search/:query")
+        node.priority.should eq(1)
+      end
+
+      it "changes when key changes" do
+        node = Node.new("a")
+        node.priority.should eq(1)
+
+        node.key = "abc"
+        node.priority.should eq(3)
+
+        node.key = "*filepath"
+        node.priority.should eq(0)
+
+        node.key = ":query"
+        node.priority.should eq(1)
+      end
+    end
+
+    describe "#sort!" do
+      it "orders children by priority" do
+        root = Node.new("/")
+        node1 = Node.new("a")
+        node2 = Node.new("bc")
+        node3 = Node.new("def")
+
+        root.children.push(node1, node2, node3)
+        root.sort!
+
+        root.children[0].should eq(node3)
+        root.children[1].should eq(node2)
+        root.children[2].should eq(node1)
+      end
+
+      it "orders catch all and named parameters lower than others" do
+        root = Node.new("/")
+        node1 = Node.new("*filepath")
+        node2 = Node.new("abc")
+        node3 = Node.new(":query")
+
+        root.children.push(node1, node2, node3)
+        root.sort!
+
+        root.children[0].should eq(node2)
+        root.children[1].should eq(node3)
+        root.children[2].should eq(node1)
+      end
+    end
+  end
+end