[WIP] Rust: Better errors

[Lukas-Dresel]

I made an initial attempt at better error messages as discussed in the slack channel. I've implemented a custom BNError type we can use to designate various different forms of errors while keeping track of dependent Errors (causes) as well as the backtrace of each error.

This does unfortunately currently rely on the unstable backtrace feature:
#![feature(backtrace)]

For now, I only modified the code in binaryview.rs to use them, I'm happy to modify the rest after some review if this is something that will be incorporated :).

[Lukas-Dresel]

I did in the meantime push the code for all uses of Err in the API if i'm not mistaken, so it should be fully testable with all API logic. Unfortunately I only have a personal license, so I can't test any headless functionality (other than that I actually get a traceable error now when trying to open_view in headless :P)

[Lukas-Dresel]

On Slack, people noted that they disliked the naming of BNError and BNResult, I am more than happy to change this, it simply persisted while I was trying to grep for old uses of Result that I had missed.

For clarification, the comments were that there is no need for the BN prefix, and we should follow the std library model of just calling them Error and Result (like, e.g., std::io does).

I personally disagree, since I dislike having to lookup up which instance of Result it is whenever I see it, however, I cede the point that following the established convention might be better, and don't mind too much since I use an IDE :P

[KyleMiles]

This is still something we want, and need to work towards resolving. No one is currently tasked on working on this, however, so we're closing this due to inactivity and will continue to track the need for this in an issue (#3245). If there's more work you want to do on this PR, feel free to reopen it.