Help: Update cmake-buildsystem documentation

Add additional information to the cmake-buildsystem manual:

* Add link to "Generator Expressions" in a place which demonstrates a
  generator expression without linking to what they are.
* Update "diagnostic message" for "Compatible Interface Properties" to
  contain an example of the message sent.
* Add information about the macOS FRAMEWORK_VERSION and how "A" is the
  conventional value to use.
1 file changed