bugfix: handle singleton in synth.exactly_one
reduce messages from transys using logger objects
home-parking example using both env and sys transition systems

This example is adapted from tulip/examples/robot_planning/robot_discrete.py
Compared to it, this is marginally realizable, because the car must remain in the lot if it is already there and the park signal is on.

Two versions are included regarding the park signal, as suggested by Necmiye Ozay:
    - park as an env atomic proposition
    - park as an env action