Add universal -trace flag to print every line of V source right before it executes

[elimisteve]

...just like bash -x myprogram.sh! Which is super useful; much more pleasant than manually adding print statements all over the place, or having to use a debugger.

I see verbose_trace in cmd/tools/modules/scripting/scripting.v, so perhaps something similar could be used to implement this?

[spytheman]

Unless we get a V interpreter, I think that will be hard to do in a general way.

[elimisteve]

It's fine if we first need to compile with -debug to build a binary that lets us -trace, which surely makes this much more feasible, yes @spytheman ?