BUG: library defines signal handler without calling previously set handlers

[solderdev]

Hi!

In board.py --> class Board --> __init__() (line 1329) a signal handler is added.
This overwrites previously defined signal handlers.
Additionally, because of this the init function may only be called in the main thread of the application.

solutions:
a)
Define a "stop()" method and do cleanup there. Best solution.

b)
When adding a signal handler with signal.signal() the old handler is returned.
Save it and call it later like this:

class Board:
  def __init__(self):
    self.prev_handler = signal.signal(signal.SIGINT, self._exit_handler)
  def _exit_handler(self, signum, frame):
    print("exit_handler")
    # do cleanup
    self.prev_handler(signum, frame)

Thank you and best regards