Improve watcher tests
Merge branch 'elixir-1.0' of github.com:tryelixir/tryelixir into elixir-1.0

* 'elixir-1.0' of github.com:tryelixir/tryelixir:
  Make travis use precompiled elixir
Make clear that permission errors come from Tryelixir
Add sandbox code
Implementation of the sandbox code, which is done by parsing the
AST before evaluating the code. Modules and local functions are
whitelisted, lists and ranges limited to a size of 100 and a user
can only redefine modules defined by him.