Joachim Wuttke authored Nov 15, 2018 and Craig Scott committed Nov 27, 2018

Extend the Synposis, and provide links to manual sections.
Add sections for `cmake --open` and `cmake --help-*`.

Introduce a new section for buildsystem generation to distinguish it
from the other functionality.  Populate it with minimal placeholder text
for now.  It will be extended later.

Co-Author: Brad King <brad.king@kitware.com>