Add Crystal version

Hi!

I want to add a Crystal version to the benchmarks. It's not the fastest, but that's what benchmarks are for :-)

In the build script I just put "crystal". To make it work you have to install Crystal as explained [here](https://github.com/manastech/crystal), then you can make a symbolic link to "bin/crystal" named crystal (I put it in /usr/local/bin/crystal).