Improved Exaple Error Handling: Replaced all calls to unwrap() in examples with either the ? operator or expect()

[sunjay]

Part of #836

This PR modifies all the examples in the examples/ folder to use more idiomatic Rust error handling code. This PR is already quite big with quite a few (hopefully small and easy to review) changes, so converting the examples in the docs will be a separate PR later.

I manually went through and ran cargo run for each example, so hopefully they all compile and CI will pass.

Everything should still work exactly the same. This PR isn't meant to change any functionality. Just updating to the latest idioms.

Some notes:

• All calls to unwrap() are completely gone from all examples
• Majority of those calls are replaced with the ? operator where possible
• Some calls could not be removed without a breaking change to the specs API, so expect() was used to keep this PR easy to merge (should be a future discussion?)
• expect() was also added in some places where it is totally fine. For example, some of the previous calls to unwrap() were for cases we expect to be unreachable. In these cases expect() is just in case something goes really wrong. (no need for future discussion)
• In addition to just calls to unwrap(), I also looked for panic!() calls and matching on Result types to find a bunch of places where code could either be improved or completely replaced with the ? operator

To make review as easy as possible, I avoided changing the structure of code as much as I could. That being said, I definitely noticed a lot of room for improvement in these examples. There is code that is starting to show its age and could be improved to be shorter, more idomatic, etc.

It's great to be able to give back to such a great library and I hope I'm able to contribute more in the future! Thanks for all your work on this! 😄

[Cobrand]

Looks good! Travis is happy as well, so I'm merging this!