Preselection for multiple choice prompts fixes #17

When calling choose with multiple outputs, a preselection can now be made for faster selection of typical answers.

For dict typed options, a list of keys is accepted, for list typed options a list of indices.

Example:

>>> options_dict = {'A': 1, 'B': 2, 'C': 3}
>>> choose("Select:", options, multi=True, preselected=['A','C'])
◉ A
◌ B
◉ C

>>> options_list = ['A', 'B', 'C']
>>> choose("Select:", options, multi=True, preselected=[0, 2])
◉ A
◌ B
◉ C