Settle on four part

Also improve reporting again using tput.
Add function writeheader
Split the image in two parts and draw them in parallel

Using job control.
Add debug functions drawcoloredline()

And some near aliases to draw black, white, red, blue and green lines.
Improve output with progressreport()
Add function drawline()
Exit after the error in sqrt.sh
Add more quoting to appease dash
yash and dash do not implement $(< file.txt)
Add the cheating_with_bc function for sqrt.sh
Rework the sqrt tests and allow different scaling factor

The environment variable $FACTOR can be used to change the scale from
1000 to anything else.

Provide testing for 1000, 10000 and 100000.
Calculate a simple sphere

Not good enough yet.
Add simple regress tests for sqrt.sh
Add simple regress tests for vec.sh
Add an optionnal argument to fixed_nearest

Enables loading arbitrary file instead of perfect_squares.txt.
Add a README and a Makefile
Simplify layout of the main script

There are already some bits exposed as library so krt.sh doesn't need to
be one.