[groff] Now online: gropdf / grops previewer

[John Gardner]

Well, here it is:

https://rawgit.com/Alhadis/Roff.js/web-demo/index.html

Some modifications were needed for web-delivery, and performance still
isn't optimal, but it works. You'll need a relatively recent browser to use
it (anything released within the last year should do).

Few things to note before you try it:

   - *This is a post-processor.* Make sure you use groff's -Z switch (or
   troff directly) if you're testing it with your own documents. You'll
   need to pipe it to your system's clipboard and paste it into the *Edit
   Source* dialogue.

   Normally, Atom handles this procedure transparently by piping the
   editor's contents through Groff in a separate process. Webpages don't have
   access to system binaries (thankfully), so this is the best I can do.

   - *Heirloom Troff output isn't perfect.* This is a known issue I intend
   to fix in a future release. At the moment, the renderer is heavily reliant
   on the ‘w’ and ‘n’ output commands to identify where a word ends. Groff
   uses these sequences consistently, but Heirloom doesn't. They're also
   omitted from certain eqn(1) constructs which also need fixing.

   - *Some fonts may look different.* Browsers handle font-rendering, which
   means the base 35 PDF fonts won't be visible in the renderer unless they've
   also been installed in your system's usual fonts directory.

   I have this taken care of by bundling
   <https://github.com/Alhadis/URW-Core35-Fonts> with the editor-package
   all 35 URW's core fonts. For the sake of your bandwidth, I've opted *not* to
   embed ~3 MBs of fonts into the page: if basic fonts seem to be missing, you
   can probably fix it by installing the fonts from upstream
   
<http://git.ghostscript.com/?p=urw-core35-fonts.git;a=tree;h=refs/heads/master;hb=refs/heads/master>
   .

   - *There's an issue with zooming.* This is what I'm stuck on, and when
   Branden offered help with matrix calculations, I decided the best way of
   explaining was with a working demo.

   If you zoom in using the *100%* menu, you'll notice you can't scroll
   left or upwards. That's because the page contents extend past the top-left
   corner of the browser window, and we all know you can't scroll past the
   window's origin corner.

Other than that, enjoy!

- John