Add ability to add base64 URI images

[ryanwersal]

From what I could tell, there didn't appear to be a direct way to add an image when using PDFKit from a browser. This adds the ability to feed a base64 encoded data URI to doc.image. I wasn't sure what the best way (or your preferred way) is to detect if we're dealing with a base64 data URI so I went with what's currently in there.

Example:

// red_dot URI from https://en.wikipedia.org/wiki/Data_URI_scheme
var red_dot = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
doc.image(red_dot, 50, 50, {
    width: 10
});

[devongovett]

Rather than checking if ';base64,' is anywhere in the string, why not use a regex to be sure the format matches exactly. For example something like this (not tested):

if m = /^data:.+\/.+;base64,(.*)$/.exec(src)
  data = new Buffer(m[1], 'base64')

[devongovett]

Looks cool. Of course, you can already add images in the browser using Buffers, or if you're using browserify, using brfs to inline your files. But this would make it easier to use base64 directly so you don't have to manually convert to a buffer every time, so I guess it's worthwhile. Check out my comment above, and I'll merge this.

[ryanwersal]

Fixed. Thanks for the info and feedback!

[devongovett]

Thanks again for the patch!