Add different output formats

[swissspidy]

As mentioned in #33, it could be useful if the warnings and messages generated by the make-pot command are available in another format, for example JSON.

This way users can programmatically run the command, easily extract the output and process it further.

My own use case would be to run wp i18n make-pot every time I push code to GitHub and import translations into GlotPress. I want to be able to send a notification if there are any wrong translator comments or anything else.

[swissspidy]

I was wondering if I could just extend WP_CLI\Loggers\Base for this and call set_logger() to keep it simple. 🤔

[swissspidy]

For my own use case it would be awesome if I could get something like this at the end:

{
  "source": "/path/to/foo-plugin/",
  "mainFile": "/path/to/foo-plugin/foo-plugin.php",
  "textdomain": "foo-plugin",
  "mergedWith": "/path/to/foo-plugin/languages/js-strings.pot",
  "destination": "/path/to/foo-plugin/languages/foo-plugin.pot",
  "extractedStrings": 127,
  "warnings": [
    {
      "type": "invalid-comment",
      "file": "/path/to/foo-plugin/src/some-file.php",
      "line": 123
    },
    {
      "type": "invalid-comment",
      "file": "/path/to/foo-plugin/src/some-file.php",
      "line": 410
    },
    {
      "type": "invalid-domain",
      "file": "/path/to/foo-plugin/src/another-file.php",
      "line": 10
    }
  ]
}