Add soft errors to minidump

[marti4d]

Fixes #31

[marti4d]

Obviously the (changes to minidump-common) need to land before this can work.

This is WIP for now, but review comments would still be appreciated. I tried to at least turn the 3 things that @gabrielesvelto pointed out into soft errors, but I also included some other stuff that I thought could be reasonably recovered from.

I didn't want to get too carried away, but I think there's probably even more stuff we could turn into soft errors... But I think this provides a good starting point!

Curious to hear what you think :)

[gabrielesvelto]

This looks very nice! I've just left a few comments.

[marti4d]

@gabrielesvelto -- I think that should address your feedback. I changed the count to "18" (whoops), made "no threads left" a soft error, and recorded soft errors from trying to restart the threads.

The only thing I'm not sure about is your ergonomics improvement suggestion. Personally, I think I like the idea of using a trait to add two new functions to Result<T, E> called something like unwrap_or_record_and_then() and unwrap_or_record_and_default(), but I'm curious to hear if you think that it's worthwhile to do this?