Moptipy

- added a first draft of an implementation of the Plant Propagation Algorithm ([PPA](https://thomasweise.github.io/moptipy/moptipy.algorithms.so.html#module-moptipy.algorithms.so.ppa))
- added the new [Op1SwapTryN](https://thomasweise.github.io/moptipy/moptipy.operators.permutations.html#module-moptipy.operators.permutations.op1_swap_try_n) operator, which is a unary operator with step size, for permutations

further improvement of end results with limits

further improved end results with virtual limits

hopefully fixed bug in end results with limit

Added Optional Limits to End Results Parsing

We added the first draft of the [OrderedChoices](https://thomasweise.github.io/moptipy/moptipy.spaces.html#module-moptipy.spaces.ordered_choices) space, corresponding [tests](https://thomasweise.github.io/moptipy/moptipy.tests.html#module-moptipy.tests.on_ordered_choices), and a [nullary search operator](https://thomasweise.github.io/moptipy/moptipy.operators.ordered_choices.html#module-moptipy.operators.ordered_choices.op0_choose_and_shuffle) for it.