InstallRules: added new variable to disable generation of install rules

The boolean variable CMAKE_SKIP_INSTALL_RULES
allows disabling generation of install rules for projects which don't
want them.
Merge topic 'optional-install' into next

4170bb2 InstallRules: added new variable to disable generation of install rules
InstallRules: remove old documentation
Merge topic 'optional-install' into next

d3780f7 InstallRules: remove old documentation
InstallRules: added new variable to disable generation of install rules

The boolean variable CMAKE_SKIP_INSTALL_RULES
allows disabling generation of install rules for projects which don't
want them.
Merge topic 'optional-install' into next

1e8d016 InstallRules: added new variable to disable generation of install rules