In the `create-react-app` command, try to install packages using Yarn.
If Yarn is not installed, use npm instead.

In `react-scripts`, detect if the project is using Yarn by checking if
a `yarn.lock` file exists. If the project is using Yarn, display all
the instructions with Yarn commands and use Yarn to install packages
in `init` and `eject` scripts.

* Exit on any errors passed in build stats

* Match console error output in start.js

* Update instructions on publishing to GitHub pages

* Update README formatting

* Extract some utilities into a separate package

* Add utils dir to `files` in package.json

* Do not create an empty `utils` dir on eject

* Load environment file via dotenv if .env file is present

* Document loading environment variables in .env file

* Minor doc tweaks

tagging dev-only code (@remove-on-publish-begin/end) and pre-eject-only code (@remove-on-eject-begin/end) #257 (#257)

* Use /static paths for assets

* Fix e2e test

* Display JS and CSS bundle sizes after build

* Print gzipped filesize, address nits

* Use filesize for human readable output.

These work regardless of whether you already have a gh-pages branch.

It has a sane default port, gzip, and doesn’t aggressively cache index.html.
Perfect.

It has gzip built-in so the size numbers are closer to real world. Thanks @ForbesLindesay for the tip!
Related to #228

This is frustrating with shells like `fish` that track directory moves

* Provide instructions on GH Pages deploy

* Add docs for GH Pages deployment

* Prevent incorrect paths in file-loader

* Minor message tweaks

* Update README.md

* Fix relative paths

* Don't assume the project is hosted at the root
* Require package.json in webpack.config.prod.js and use homepage if set; otherwise use '/'

* Fix package.json path and add sample package.json for tests

* Update publicPath to use relative path portion of URL defined in homepage

* Update successful bundle generation message

* Show bundle generation success message based on presence of homepage in package.json

This ensures errors are not tolerated.
Otherwise, Webpack just builds an empty bundle.