[PythonCAD] New tangent stuff added

[Art Haas]

Hi.

PythonCAD now handles drawing tangent circles between an existing
construction circle and a construction line, or two construction lines.
Also I've added the ability to draw tangent construction lines between
two construction circles. These routines can still use some more polish,
but they work. I've uploaded the code to the public repository.

I was trying to get a release done tomorrow, but it looks like the next
release will be in the first week of June. I'm looking at adding work
contributed to PythonCAD by David Broadwell so that the entry box is
used more to invoke drawing operations. I have to try and learn a little
bit more about handling widget focus so that this stuff works nicely.

Art
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