New feature: draw arcs & solid arcs

[Lucas-C]

One or two new methods could be added to FPDF,
similarly to the existing, rect(), circle(), or ellipse()

Inspiration could be taken from HexaPDF

[Lucas-C]

Implemented in #266

Thanks @tabarnhack!

[gettalong]

@Lucas-C Nice that you draw inspiration from HexaPDF 😁

I just saw the example output at https://pyfpdf.github.io/fpdf2/Shapes.html and wanted to note that the lines joining at the center of the green solid arc are not joined correctly. You can see artifacts sticking out:

HexaPDF renders this arc like this:

So you might wanna draw the whole solid arc with one continuous path instead of multiple.

[Lucas-C]

Thank you @gettalong!

At first, I thought that in order to fix this we would need to implement PDF Line Join Styles,
but in fact I think we should imply use the h path operator intead of closing arcs with a line using l:
https://github.com/PyFPDF/fpdf2/blob/2.5.5/fpdf/fpdf.py#L1651

We should open a dedicated "bug" issue explaining the problem and how to solve it in arc() in solid_arc() methods

[gettalong]

Yeah, that could also be the reason and would certainly be easier.

[Lucas-C]

I opened #488