Suggestion: add the first four bytes from the stack top to the trace

[Ptival]

I'm currently debugging a problem with my emulator where it appears we don't pop the same value from the stack.

This is in general not super practical to debug as I don't know how far before we started disagreeing on the stack state. I think it'd be nice to have a small fragment of the stack on the trace.

[robert]

Sounds reasonable, want to try a PR? Maybe with a --with_stack argument so people can choose not to use this.