check for PYENV_ROOT.
the exit code (1) means aborting.
add simple testing which aim for protection checking.
add test_helper to debug in a temporary directory.
add a scaffold path into test_helper.
testing the virtualenv name picker.
configure travis-ci.
it seems more debug information is useful.
okay. then create the virtualenvs directory.
add build badge in README.
Merge branch 'tests' and close #1