Add compilation status and error/warning count to the error message formatter

[astorije]

In many cases, displaying the error message is not helpful. In our case, we barely display enough of the filepath to help use figure out what is failing, so an error count would actually be a lot more concise and helpful, indicating the developer to take a look to their console.

This change allows for the following notifications:

Using the following configuration:

// webpack.config.ts
import WebpackBuildNotifierPlugin from 'webpack-build-notifier';

let address: string;

export default {
  // ... snip ...
  plugins: [
    // ... snip ...
    new WebpackBuildNotifierPlugin({
      formatMessage(_error, _filepath, status, errorCount) {
        return `${errorCount} ${status}${errorCount === 1 ? '' : 's'}`;
      },
    }),
  ],
  // ... snip ...
};

This will conflict with #67 but I'm happy to rebase either PR on merge of the other one should you be happy with them :)

[coveralls]

Pull Request Test Coverage Report for Build 144

• 14 of 14 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 93.636%

---

Totals
Change from base Build 118:	0.5%
Covered Lines:	130
Relevant Lines:	134

---

💛 - Coveralls

[RoccoC]

Thanks for the PR! Approved and merged. I'll release a new version with your change shortly.

[astorije]

Excellent, thanks! I'm going to fix conflicts on my other PRs then 🙏

[RoccoC]

Released in 2.2.0