Allow a single mod version to support multiple factorio versions

[Hanse00]

Perhaps this has been discussed in the past, and I was unable to find it. If that's the case, my bad.

I'd like to see my mod be able to support multiple factorio versions out of the box, by making the "factorio_version" variable in the info.json a list.
This is so that, in those cases where factorio version don't change the modding API in any ways I'm using it, I'd be able to maintain the same codebase across multiple versions.

The alternative (as it currently is) is that I must do one of two:
* Stop supporting older factorio versions - Whilst this is fine once a version reaches stability perhaps, during the early phases of a new version, I want to be able to maintain compatibility with the older version that most people are still playing, whilst supporting the new.
* Maintain multiple versions - I can do something smart with bash to build multiple versions of the mod, with different "factorio_version" values, and different version numbers, and distribute those. But that's quite a hassle.

[Squelch]

We are currently discussing this very thing over here