Catch exceptions from user callbacks early

[paullouisageneau]

This PR introduces try catch blocks to ensure exceptions leaking from user callbacks are caught early, otherwise in some situations it could introduce undesired behavior changes like a second callback not called as it should.

[themightyoarfish]

Would it be possible to install some kind of exception handler? I've been repeatedly bitten by my errors getting swallowed and it taking a while for me to remember that all exceptions in user callbacks get caught. Now I have to remember to enable logging and then crawl it during development.

[paullouisageneau]

@themightyoarfish I get the idea but do you really need a dedicated callback for that? Uncaught exceptions result in warnings that you can easily intercept in the log callback.