Add tests

To start:

• Unit tests using xonsh syntax

• Xonsh tests

• Xxh Development Environment with tests

• click tests

  This is working but result.output is not captured:

  from click.testing import CliRunner
  from xonsh_awesome_cli_app.cli import cli
  
  def test_say():
    runner = CliRunner()
    result = runner.invoke(cli, ['--name', 'Peter', 'say', 'hello'])
    # assert result.exit_code == 0
    assert result.output == 'Peter say: hello\n'
  

  pytest tests/