Add Crystal programming language

Language homepage: http://crystal-lang.org
Source code: https://github.com/manastech/crystal

readme.md

@@ -48,6 +48,7 @@
 - [Go](https://github.com/avelino/awesome-go)
 - [Scala](https://github.com/lauris/awesome-scala)
 - [Ruby](https://github.com/markets/awesome-ruby)
+- [Crystal](https://github.com/veelenga/awesome-crystal)
 - [Clojure](https://github.com/razum2um/awesome-clojure)
 - [Elixir](https://github.com/h4cc/awesome-elixir)
 - [Elm](https://github.com/isRuslan/awesome-elm)