Kerning support

[RGBz]

It doesn't look like kerning information is used with ASM or OTF fonts. Both examples below show gaps between the A and the V:

const fs = require('fs');
const pdf = require('pdfjs');
const openSans = new pdf.Font(fs.readFileSync('pdfjs/test/fixtures/font/opensans/bold.ttf'));
const times = new pdf.Font(require('pdfjs/font/Times-Bold.json'));

const doc = new pdf.Document({ font: times, padding: 10 });
doc.pipe(fs.createWriteStream('output.pdf'));

doc.text('AVA', { font: times });
doc.text('AVA', { font: openSans });

doc.end();

[rkusa]

Yes, this is unfortunately currently not supported. While the kerning offset is already read (https://github.com/rkusa/pdfjs/blob/master/lib/font/otf.js#L55) the correct placement within the PDF document is not implemented. Since this is something just recently requested from customers of the application where I am using this library, I might have a look at it soon.

[rkusa]

I've implemented kerning. Please let me know if you see anything strange. There is still one limitation, the kerning does not yet work when appending text, e.g.

doc.text('A').append('VA');

[RGBz]

Great thanks! I tested it out and it seems this fixed kerning for ASM, but not OTF. After some diving, I think this PR should get OTF to work as well: #84