change some doc examples to iex style
fix typo
Merge pull request #2847 from jw2013/doc-iex

change some doc examples to iex style
Merge pull request #2848 from jw2013/iex-typo

fix typo
Use elixir tmp directory instead of /tmp, closes #2849
Merge branch 'master' of https://github.com/elixir-lang/elixir