Help: Update cmake-buildsystem documentation
Add additional information to the cmake-buildsystem ReStructuredText file.
- 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.
Edited by Brad King