[WIP] Add elixir client (#4675)

* Add elixir client

* Add test for elixir client

* Add shell script for generating sample codes for elixir client

It just copied from bin/bash-petstore.sh

* Make elixir-petstore.sh to generate sample codes for elixir client

* Add sample codes for elixir client

bin/elixir-petstore.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+
+SCRIPT="$0"
+
+while [ -h "$SCRIPT" ] ; do
+  ls=`ls -ld "$SCRIPT"`
+  link=`expr "$ls" : '.*-> \(.*\)$'`
+  if expr "$link" : '/.*' > /dev/null; then
+    SCRIPT="$link"
+  else
+    SCRIPT=`dirname "$SCRIPT"`/"$link"
+  fi
+done
+
+if [ ! -d "${APP_DIR}" ]; then
+  APP_DIR=`dirname "$SCRIPT"`/..
+  APP_DIR=`cd "${APP_DIR}"; pwd`
+fi
+
+executable="./modules/swagger-codegen-cli/target/swagger-codegen-cli.jar"
+
+if [ ! -f "$executable" ]
+then
+  mvn clean package
+fi
+
+# if you've executed sbt assembly previously it will use that instead.
+export JAVA_OPTS="${JAVA_OPTS} -XX:MaxPermSize=256M -Xmx1024M -DloggerPath=conf/log4j.properties"
+args="$@ generate -t modules/swagger-codegen/src/main/resources/elixir -i modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml -l elixir -o samples/client/petstore/elixir"
+
+java $JAVA_OPTS -jar $executable $args