Implement option to embed fonts

[ThomasTJdev]

This PR adds the ability to embed fonts directly into the generated PDF files.

Embedding increases the PDF file size slightly, but enables much better post-processing compatibility - especially when copying text or handling non-ASCII characters.

This also solves my issue from 2021 :) #39

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Example

To enable font embedding, simply set the new option:

var opts = newPDFOptions()
opts.setEmbedFont(true)

var doc = newPDF(opts)

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Notes

I've aimed to keep the implementation as non-intrusive as possible, but it will always load the font cache in the makeTTFont().

[jangko]

embedFont should passed through setFont, then the table initialization is done once in makeFont.
I prefer users have liberty to choose which font they want to embed. And for the global embedFont flag,
it will override the setFont's embedFont flag.

Built in font have no effect when setting this font.

[ThomasTJdev]

I understand. During my testing I used some more fonts from the demo folder an got in trouble with the width, so that's the first commit #da483d4.

For the setFont() I added an embedFont: bool and got it to work partially, so the font got embedded (copy-paste'able) but the rendering broke. So I'm gonna pass on that one for now.