Use Mix.Version for dependencies
Require `override: true` option to override a dep
Projects without a mix.exs can't be recursive

Otherwise, recursive_enabled? always returns true, even
when it should be disabled, affecting the output of tasks.

Closes #1374
Minor doc fix
Merge pull request #1376 from ericmj/mix-deps-version

Use Mix.Version for dependencies
Replace ?is_new_atom macro by ?is_atom_start
inspect_kw no longer is
Ensure Stream.take/2 halts execution
Refactor IEx.Options and raise on bad key
Merge pull request #1389 from alco/iex-options-fix

Refactor IEx.Options and raise on bad key
Small refactoring on IEx.Options