* generates hello_world.txt.gz file - fixes #235
* highlights the difference between gzdecoder-bufread and -read examples

* Make Clippy happier, minor cleanups

I ran `cargo clippy` and addressed some issues it raised, while leaving other issues for another time. Hopefully this will make this code a bit easier for newcomers to read.

Biggest changes:
* `foo.len() > 0` ➡ `!foo.is_empty()`
* `return x;` ➡ `x`
* `{ foo: foo }` ➡ `{ foo }`
* adding a few `Default` trait implementations
* some `match` statement cleanup

Also, fixed two `ffi::uInt::max_value()` ➡ `ffi::uInt::MAX` due to deprecation.

Biggest TODOs (please give feedback if they should be fixed too):
* Clippy has complained about many `foo >> 0` -- which is a noop that might confuse (?)
* some other corner cases that I don't know enough about

* cargo fmt

* Spellchecking comments, rm trailing spaces

* revert vendor file changes

* Update to miniz_oxide 0.5

* Update to quickcheck 1.0 / rand 0.8

* ci: Pin Windows version to 2019 instead of latest