Added another building block program. This program will be required
going forward in other modules. `version_at_least` takes two version
numbers and returns true if the second is higher than the first.
That means primarily it is useful to check if a program fulfills a
minimum required version, e.g.: `version_at_least 2.1 $(my_program -v)`.
Will be primarily useful for git version checking in the near future.
It has a second possibility of checking for ordered version numbers
passed in but this is of less use. Check source for more information.
