Updates to enhance GitHub Actions continuous integration:
* ci: add macOS app bundle packaging using cargo-bundle, closes#352
based on https://github.com/EndlessSkyCommunity/ESLauncher2/blob/master/Cargo.toml
* ci: add web target, building using wasm-pack (for #446)
* ci: refactor and cleanup targets, split out instead of using matrix
* main: save config in consistent OS-specific dirs::config_dir()
Instead of storing and loading in the current working directory, change
to a consistent dedicated configuration directory. This is necessary for
.app launching since cwd is set to /. To preserve compatibility with
existing installations, if conf.cfg exists in cwd then it will be used instead,
but otherwise we will use the operating system specific config dirs:
// Lin: Some(/home/alice/.config)
// Win: Some(C:\Users\Alice\AppData\Roaming)
// Mac: Some(/Users/Alice/Library/Application Support)
* macos: add icons based on screenshotted logo
* macos: add Cmd-Q to quit
* Closes#237 Bump base64 from 0.10.1 to 0.11.0
* Closes#241 Bump flate2 from 1.0.12 to 1.0.13
* Closes#245 Bump num-traits from 0.2.8 to 0.2.10
* Closes#248 Bump serde_json from 1.0.41 to 1.0.44
* Closes#249 Bump serde from 1.0.102 to 1.0.104
* Closes#251 Bump web-sys from 0.3.30 to 0.3.33
* Closes#254 Bump structopt from 0.3.3 to 0.3.7
* Bump cfg-if from 0.1.9 to 0.1.10
* `cargo update` all modules
ice_iix