Phpinsights: Add checkstyle formatter

[Gummibeer]

| Q | A
| ---------------- | -----
| Bug report? | no
| Feature request? | yes
| Library version | latest

ScrutinizerCI supports custom commands if they produce a XML file in checkstyle format.
This would allow to see the phpinsights "errors" in the ScrutinizerCI web UI instead of scrolling through the TravisCI/CircleCI logs.

https://scrutinizer-ci.com/docs/tools/custom-commands/

[Jibbarth]

Great news ! It's already implemented => PR #271

However, it's not released yet. Could you try with dev-master version ?

[Gummibeer]

Ah, cool. Will Test it tomorrow. Thanks!

[Gummibeer]

@Jibbarth it's missing in the console help description.
https://github.com/nunomaduro/phpinsights/blob/9b0418e31641febfc4c9a111d9b91259ab35c38f/src/Application/Console/Definitions/AnalyseDefinition.php#L66-L72

encoding="UTF-8" is missing in the opening <?xml?> tag.

It should be noted that the file paths are relative to the path given to analyse command and not to the XML file, which is okay/logical because no file is created by command.

[dmitryuk]

@Gummibeer your remarks are fixed in the PR. Please try again )