* restore elixir petstore original from codegen2x
* update elixir generator to work with oas2
* minor fix to elixir generato
* minor enhancement to templates
* update elixir petstore with oas2
* 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