Depending on specific Package and TPL versions

[wawiesel]

Each dependency on a package or TPL needs a way to specify a version. I am thinking something like this

botgPackageDependencies(
    LIB_REQUIRED_PACKAGES
        Testing123[v=LATEST]
        HioH[v=STABLE]
        BootsOnTheGround_LAPACK[v<1.2]  
)

There could be a sequence of expressions like v>=1.0,v<1.2 and every package dependency could have this. The repository for the package is then checked out at a particular tag corresponding to the VERSION in the form, e.g. v1.1.17. For TPLS, it's a little trickier in that we need BOTG to be able to report the found version if it finds it on the system or require a version from HUNTER if it resorts to downloading. There of course should be an algorithm that analyzes all the version constraints and determines the optimal, as well as determine if that exists on the repository and report a reasonable error. There should also be a way to specify a fixed version from the CMake CLI to use for a package. This would be helpful when updating versions, i.e. kick off a test run with that single change.