Viridis color maps for awk

Provides functions with the form:

	to_<color map>_<format>(_min, _max, x)

where, <color map> is either viridis or cividis
and <format> is either hex (e.g. "#767676") or ps (e.g. "0.239 0.302 0.541").

Link somewhere convenient:

	ln -s `pwd`/viridis.awk $HOME/lib/

Then call from a second progfile:

	awk -f $HOME/lib/viridis.awk -f examples/heatmap.awk examples/lena > heatmap.ps