Add automatic debug logs

[xs5871]

Automatically enable debug output if a serial monitor is connected to the serial interface.

[regicidalplutophage]

Cautiously approving this.
Since most people only learn about boot.py when something is not going well for them, I wonder if this doesn't affect performance too much.

[xs5871]

Boot configuration doesn't really affect this. If the serial console is disabled, then of course no debug messages are processed. If, as by default, the serial endpoint is connected: if and only if a serial monitor is actually connected (picocom, screen, etc.) debug messages are enabled. They are disabled again once the monitor is properly disconnected/closed.
There's one stumbling block where a serial monitor can be closed without resetting the connection (in picocom that's ctrl-q vs. ctrl-x) -- but that'll only happen if debugging was enabled intentionally in the first place. That's a reasonable trade-off for the convenience in my opinion and shouldn't affect any casual users.
Does this explanation address your concerns? I'll wait with the merge for your feedback.

[regicidalplutophage]

U-huh, I misunderstood it then.
All good, I don't have any issues with this 👍