Smart processing of 'headerParserRegex' property

[AlexPl292]

Hi! In continuation of #11

In my opinion new Regex doesn't look really "declarative" for Gradle configuration. I suggest to add smart processing of 'headerParserRegex' property: if this property is a regex - leave it as it is. If it's a string - convert it to the regex.

Unfortunately, I wasn't able to find a test that uses headerParserRegexProperty directly.

[hsz]

Thanks, I like that approach!
I had to adjust your implementation because headerParserRegexProperty is not available via Gradle configuration, but headerParserRegex.