Switch error handling setup to quick_main! macro from error-chain

[brson]

Right now the error handling pattern suggested by the cookbook's 'about' page, and used in at least some of the examples, looks similar to quick_main!. Seems like we should just use that.

Switch the existing examples to replace 'main' with 'quick_main!', and update the about page.

cc @dtolnay @Yamakaky

[Yamakaky]

quick_main! was maid for that usecase ^^

[Yamakaky]

quick_main! was maid for that usecase ^^

I can do that

[budziq]

Using following form will hide part of doctest boilerplate from rendering but still allow for the code to compile and run under skeptic.

```
# fn main() {
#    run().unwrap();
# }
```

It might make the existing snippets more ergonomic without the need to pull error-chain as dependency (or even hide error-chain noise if required)

cc @brson

[dtolnay]

Given that we don't have playground links (see #32), there needs to be a way to copy and run these examples. I would prefer not to hide main so that you can copy into a main.rs and expect it to work.

[brson]

Yes, I want to not hide code in the cookbook, have the examples say everything they are doing.