Add support for Antlr4 grammars

[matthiasbalke]

I'm working on an integration of antlr/Antlr4Formatter by @teverett. The formatter is in an early stage, but already formats Antlr4 grammars.

I started with the Gradle Plugin integration, but once thats done, would be willing to add support to Maven too. I'll push my current status within today, so we can talk about things that need to be done.

[jbduncan]

Sounds neat to me!

I used ANTLR when I was working on my dissertation a couple of years ago, so having an ANTLR grammar formatter included by default in Spotless sounds interesting to me.

I look forward to whatever work towards this that you manage to make. 👍

[matthiasbalke]

@jbduncan Check out PR #273. The integration is complete and works. But the formatter library itself is getting fixed in the meantime.

[jbduncan]

Cheers @matthiasbalke! I'd be more than happy to review it when you're ready. :)

[nedtwigg]

Released in plugin-maven 2.0.0 and plugin-gradle 4.5.0.