Make LUE Conda packages from custom channel play nice with releases on conda-forge channel

[kordejong]

During development the custom Conda channel is regularly updated with Conda packages for the current development version. Currently, the version number of this development version is the same as the upcoming official release. This will likely result in conflicts when people want to switch from the development version to the official version.

On idea is to bump the tweak version number for development releases that are newer than the currently released version. So, when the currently released version is 0.3.7, the development version would be numbered 0.3.7.1, for example. This tweak number, which is supported by CMake, can be increased at will, but I don't think this is crucial. What is crucial is that new releases have a higher version number than the development versions released before that.

I don't know whether / how Conda will deal with tweak versions, but it seems worth trying out.

When we start using the version tweak, we need to visit all code that deals with versions. See also version.{hpp,cpp.in} in source/shared.