Improve version number handling.

[vaillancourt]

• Add more formal distinct numbers for the version, allowing better comparison when building against multiple versions of the library.
• Add the "next version" as a "patch" value to make this useful (when comparing version 0.16.X against "master")
  • This value needs to be updated once a new version has been produced.

[vaillancourt]

The reason I've created this is that we're currently at 0.16.2, and I noticed a specific change in behaviour in our software when "just moving" to 0.16.6. To help diagnose things and adapt some behaviour (in our case, something related to multi-threading), better handling of the version would help a lot.

I've applied the same change to all the versions until 0.16.2 (see my branches), but I don't think anything within the current project's infrastructure that allow to apply such a thing.

So I suppose this is essentially to help "future us".