Allow specification of minimum cmake version

[Justin-Johnson]

It looks like the minimum cmake version is baked into the generated cmake:

cmake_minimum_required(VERSION 3.4)

The latest build of CLion doesn't support cmake versions < 3.5 so it's complaining.

Ideally there'd be a command line option or such to specify the minimum cmake required in the generated cmake file.

[TaimBak]

Having the same issue with Xcode.