*Please note:* While following the steps in the README still works with this patch, in the sense that the example runs and successfully renders a PDF document, I unfortunately cannot tell if it illustrates Webpack best practices.
This resolves an issue I had when loading pdf.js with webpack. `pdfjsLib` was always `undefined` after the import, and I dug deep into pdf.js's `webpack.js` file to sort out this issue, making all sorts of changes.
I figured out that there was just something wrong with the export/import procedure. After making this change, I now have the full pdfjs object in my webpack application.
Since we really don't want to let a particular Webpack-mode dictate how we can/can't write code, let's add a note in the webpack-example README about minification instead.
Using `require.resolve("worker-loader")` to check if `worker-loader` is installed causes webpack to include `worker-loader` in the output bundle, which is not the intended effect. Aside from increasing the bundle size unnecessarily, it also causes errors for webpack configs with targets that don't have node's built-in modules.
These errors can be fixed by configuring webpack `externals` to exclude `worker-loader`, but it's more difficult to figure out this solution than to figure out that `worker-loader` needs to be installed (even without this explicit error message).
To solve this, the explicit check for `worker-loader` has been removed. An alternative solution would be to use webpack's `resolveWeak`. Documentation has also been added in `examples/webpack` to help users.
Previously the commands were not properly parsed as such by GitHub
because they need to be indented with four spaces.
Furthermore, address some minor textual nits.
