clrstrip: place contents into a full width colour strip

Copyright (C) 2018-2020 by Jonathan P. Spratte

This package may be distributed and/or modified under the conditions of the
LaTeX Project Public License (LPPL), either version 1.3c of this license or (at
your option) any later version.  The latest version of this license is in the
file

  https://www.latex-project.org/lppl.txt

The package provides

 - `\colorstripSet{<key=value>}`: set options outside of the environment
 - `colorstrip`: an environment taking the arguments
    `[<color model>]{<color>}[<key=value>]` and outputting its contents inside
    of a coloured strip spanning from one page border to the other.