Add crystal

crystal/Dockerfile

@@ -0,0 +1,14 @@
+FROM ubuntu:xenial
+
+RUN \
+  apt-get update && \
+  apt-get install -y apt-transport-https && \
+  apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 09617FD37CC06B54 && \
+  echo "deb https://dist.crystal-lang.org/apt crystal main" > /etc/apt/sources.list.d/crystal.list && \
+  apt-get update && \
+  apt-get install -y crystal gcc pkg-config libssl-dev libxml2-dev libyaml-dev libgmp-dev git make && \
+  apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+WORKDIR /opt/crystal
+
+CMD ["bash"]