Add VERSION constant for runtime usage

Introduce `Radix::VERSION` to be used at runtime by users of the
library for any purpose this will help them (expose them, use
conditional blocks or similar).

Also add spec that checks that defined versions in both `shard.yml`
and `Radix::VERSION` matches to avoid messing up releases.

CHANGELOG.md

@@ -5,6 +5,8 @@ This project aims to comply with [Semantic Versioning](http://semver.org/),
 so please check *Changed* and *Removed* notes before upgrading.
 
 ## [Unreleased]
+### Added
+- Introduce `Radix::VERSION` so library version can be used at runtime.
 
 ## [0.3.0] - 2016-04-16
 ### Fixed

spec/radix/version_spec.cr

@@ -0,0 +1,14 @@
+require "../spec_helper"
+require "yaml"
+
+module Radix
+  describe VERSION do
+    it "matches version defined in shard.yml" do
+      contents = File.read(File.expand_path("../../../shard.yml", __FILE__))
+      meta = YAML.parse(contents)
+
+      meta["version"]?.should_not be_falsey
+      Radix::VERSION.should eq(meta["version"].as_s)
+    end
+  end
+end

src/radix.cr

@@ -1 +1,2 @@
 require "./radix/tree"
+require "./radix/version"

src/radix/version.cr

@@ -0,0 +1,3 @@
+module Radix
+  VERSION = "0.3.0"
+end