Merge that branch into current branch

    fast_forward and commit add the eponymous options to the command

def merge(branch, fast_forward=False, commit=True, options=None):
    """Merge that branch into current branch

    fast_forward and commit add the eponymous options to the command
    """
    more_options = [
        fast_forward and '--ff' or '--no-ff',
        commit and '--commit' or '--no-commit',
    ] + (options and options or [])
    option_string = ' '.join(more_options)
    all_branches = branches()
    assert branch in all_branches, 'Missing branch: %s' % branch
    command = 'merge %s %s' % (option_string, branch)
    return run(command)