pythagorean complement proportion valuenode function
f(x)=sqrt(1/x^2-1)
if x=0, f(x)=9999.0
if abs(x)>1, f(x)=0

Linux instructions:

1. Download synfig code as directed in:
https://synfig-docs-dev.readthedocs.io/en/latest/building/Preparing%20Environment.html

2. Copy the cpp and h files in:
synfig-core/src/synfig/valuenodes

3. Add the cpp and/or h filenames in (after valuenode_pow.*)
synfig-core/po/POTFILES.in
synfig-core/src/synfig/valuenodes/CMakeLists.txt
synfig-core/src/synfig/valuenodes/Makefile_insert

4. Compile and run synfig as directed in:
https://synfig-docs-dev.readthedocs.io/en/latest/building/Building%20using%20Autotools.html

5. Open foreshortening_demo2.sifz

6. Select the bone, use the "Length handle" to shorten the bone.

7. You should see an ellipse at the end of the rectangle, which should increase and decrease like a cylinder base
