Loaders:

- transform the import

- loaders is a list and processing is from RIGHT to LEFT.

- file loader does not work wit svg-sprite-loader.
but default storybook has it so we need to exclude it

- loader accept a string

What is file loader?

The file-loader resolves import/require() on a file into a url and emits the file into the output directory.

> after file loader, the content of file is converted to
"module.exports = __webpack_public_path__ + "static/media/dollar.613ee179.svg";"

1. file-loader 
   https://github.com/webpack-contrib/file-loader

2. 1. Emit the file with good hash name
      Output file is configure by webpack configure
      output: {  path:}

   2. Replace url(xxx) by publicPath/hash
      pubic path is configure in webpage.output.publicPath

Tricks:

- loader are not minimized, change the loader code directly to log info