Create an example script that changes global settings

This script serves as an example and a test of changing global
settings in a dialog script.  Normally we change these settings within
the ‘src/settings.lua’ file.  But because of the way LNVL loads these
scripts it is possible to change some settings in a script itself
before we create any objects that rely on those settings, like
Scene objects.
Describe changing global settings in scripts in the Howto guide
Merge branch 'global-settings-in-scripts'

* global-settings-in-scripts:
  Describe changing global settings in scripts in the Howto guide
  Create an example script that changes global settings