Improve svg rendering

[z3dev]

These changes improve the 'rendering' of designs exported to SVG.

• set defaults for fill, fill-rule, stroke-width at the SVG level
• remove above from path serialization
• corrected fill color for continuous paths (geom2)
• added support for special attributes; id and class

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[z3dev]

@hrgdavor please review / try if you have time. I think these changes will help users when exporting to SVG.

[z3dev]

See #558 for how to add a ‘name’ to objects. Probably, support for ‘id’ and ‘class’ is enough.

[hrgdavor]

np. I will take a look a bit and test

[hrgdavor]

It will be few days before I can do so, I am traveling today and tomorrow, so I can't test this right away

[hrgdavor]

I have been playing with it, and it looks good in the svg source. I am not a fan of using fill.

While jscad renders lines

the svg export uses fill

personally I would prefer stroke

[hrgdavor]

I have some complaint/proposals that are unrelated to this PR.

jscad is generating poly for each curve immediately, so an export to SVG is a poly instead of circle, arc, besier.

Without changing jscad core, one option would be to explore integration with other 2d libs like maker.js ... actually all that is needed is to improve require in the future because V2 now allows us to script with any valid JS lib.

[hrgdavor]

It is a good step forward.