adjusting-spacing: change interface and name

The function no longer takes a moment as it's argument,
but an ordinary number. This should make it more user-friendly.

I've changed name because when it was a noun it sounded like
a name of a property that should be overridden, rather than
a function name.
adjusting-spacing: fix special character
adjusting-spacing: add predefined commands
adjusting-spacing: add documentation. status=official