Resolve #1 "Port Interface", #8 "Port Coupling"

Adds:

• Port interface functions for InputPort and OutputPort.
• Functionality for connecting ports and signals, both via signals and ports.
• Tests that verifies that the functionality has been correctly implemented.
• Fixes to older code so that it works with the new interfaces.
• Minor functionality for connecting operations in their constructors.

Closes #1 (closed) and closes #8 (closed)

b_asic/port.py

@@ -164,7 +164,7 @@ class OutputPort(Port):
         return len(self._signals)
 
     def connect_port(self, port: InputPort) -> Signal:
-        return = Signal(self, port)      # Signal is added to self._signals in signal constructor
+        return Signal(self, port)      # Signal is added to self._signals in signal constructor
 
     def connect_signal(self, signal: Signal) -> None:
         assert not self.is_connected_to_signal(signal), \