improved prompt
Merge branch 'feature/better_prompt_support' of github.com:saxix/cookiecutter into feature/better_prompt_support

* 'feature/better_prompt_support' of github.com:saxix/cookiecutter:
  improved prompt
improved interpolation
cleanup tests
Style cleanup.
add ability to merge os.environ variables in prompt
Merge branch 'feature/better_prompt_support' into work

* feature/better_prompt_support:
  add ability to merge os.environ variables in prompt
  Style cleanup.
  cleanup tests
  improved interpolation
  improved prompt

Conflicts:
	cookiecutter/prompt.py
	tests/test_prompt.py