sweep: fix examples, add documentation

[wpfff]

currently the examples seem to not match the current call signatures, and imports aren't working properly. To get anything to work, reading the source is basically mandatory.
Examples:

• basic_exaple_with_convenience_functions.ipynb: do_experiment(setup, sweep_object, cleanup) does not seem to be the correct call signature for do_experiment.
• basic_example_without_convenience_functions.ipynb: from pytopo.sweep.base import ParameterSweep, ParameterWrapper, Nest, Chain does not work.

We need to maintain working examples and documentation. all docs need to be checked.