Generate svg schematics for KiCAD v6,7 libraries

[jemathews0]

fixes #167

The following branch allows the generate_svg() function to work properly with a KiCAD version 7 (and probably version 6) library, but I need some feedback on a few things before I think it's ready to merge:

1. I noticed that there is a generate_schematic() function and wonder whether generate_svg() is going to be obsolete.
2. I have tried running the unit tests, but I am still new to pytest and I can't find the generated .svg files to see if they're correct
3. The generated svg files still have some strange bends/jogs in the lines that I can't seem to get rid of. I've tried reducing the bounding box so the pins stick out just a little bit, and removing/adding the part labels to the bounding box, but to no effect. As far as I can tell, the side parameter has been set correctly. It can be visualized by uncommenting tools/kicad/v6.py:961 and then generating the svg. Some of these jogs are very annoying because they cause the lines to go through multiple pins on the same part so it's unclear to which pin the wire is connected.
4. I considered switching to use an svg library instead of manually writing the svg code as was done for v5, but I decided against it.
5. I modified things so that all the scaling and flipping from symtx is done using a <g> transform() <g/> tag enclosing the svg at the exact scale and orientation indicated by the library. I felt this was a little cleaner but others might disagree.

[tapegoji]

do you have generate_schematic too?

[jemathews0]

do you have generate_schematic too?

No. I never messed with generate_schematic.