Coloured output :rainbow:!

Requires rainbowrite (https://github.com/richfitz/rainbowrite), and
like all terminal colouring things requires a terminal emulator
requires a colour-capable terminal.  The R console (Rgui) and Rstudio
do not allow this.  But this does work in an actual terminal (either
from within R or the standalone command line version of maker).

Support for other terminals should be added to rainbowrite.  It does
look like emacs terminal is not supported.