Add support for TTC collections

[jamis]

This PR depends on prawnpdf/ttfunk#33 (which adds the underlying TTC support to TTFunk).

The TTC support in Prawn mirrors the approach taken with the DFont collections, requiring users to specify which font they want from the collection via the :font key. It does not currently allow you to specify fonts by name, but requires you to specify them by numeric index within the file.

A simple program demonstrating usage:

require 'prawn'

LucidaGrandeSrc = '/System/Library/Fonts/LucidaGrande.ttc'.freeze
LucidaGrande = {
  normal: {
    file: LucidaGrandeSrc,
    font: 0
  },

  bold: {
    file: LucidaGrandeSrc,
    font: 1
  }
}.freeze

Prawn::Document.generate('ttc.pdf') do |pdf|
  pdf.font_families['LucidaGrande'] = LucidaGrande

  pdf.font 'LucidaGrande'
  pdf.text 'Hello, World! 12345'
  pdf.text 'Hello, World! 12345', style: :bold
end

[jamis]

(to be clear -- the CI check is failing because of the dependency on my branch of ttfunk)

[juanfal]

The answer to this program from ruby

mb10:10:57 Desktop $ ruby -v
ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin16]
mb10:11:01 Desktop $ ruby testPrawn.rb 
/usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/font/afm.rb:48:in `initialize': /System/Library/Fonts/LucidaGrande.ttc is not a known font. (Prawn::Errors::UnknownFont)
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/font.rb:289:in `new'
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/font.rb:289:in `load'
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/font.rb:243:in `find_font'
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/font.rb:57:in `font'
    from testPrawn.rb:23:in `block in <main>'
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/document.rb:226:in `initialize'
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/document.rb:142:in `new'
    from /usr/local/lib/ruby/gems/2.4.0/gems/prawn-2.1.0/lib/prawn/document.rb:142:in `generate'
    from testPrawn.rb:20:in `<main>'

[jamis]

@juanfal -- it looks like you're using the prawn gem (see the backtrace, it's loading prawn 2.1.0 in the gems directory). This pull request is not yet released (and in fact has not yet been merged or--to my knowledge--reviewed). If you want to test this PR, you'll need to check out the ttc-support branch of my fork of Prawn, as well as my ttc-support branch of my fork of TTFunk.

[pointlessone]

This is not quite an appropriate name for the method. If you want to follow inheritance path I'd suggest renaming the method to something less specific. For instance, read_file.

[jamis]

It may not be appropriate...but it's an inherited method from the superclass that is being overridden in the subclass. You can see that the dfont.rb implementation overrides it, too. You're right that the name is misleading, but as it was already named this before, it seems that refactoring it might be out of scope for this pull request.

[pointlessone]

Prawn uses git to track code changes and thus authorship information. Given the nature of a highly collaborative project such a Prawn, this information can get outdated rather quickly. Because of this I'd suggest leaving this comment out.

We acknowledge your contribution and you definitely keep copyright for the code.

If you feel strongly about inclusion of this comment please update it to be factually correct as of now.

[jamis]

Ha, sorry... as you can see from the date, that was actually not recent. :) I copied the font/dfont.rb file (which I also contributed, more than eight years ago, apparently!) and adapted it to TTC, and forgot to clean up the header comment. I'll clean it up there, and on dfont.rb.

[pointlessone]

Fonts are usually referred to by name, not index. :font doesn't seem to be appropriate. Maybe rename the argument to :index?

[jamis]

Yeah, :font is not the best name when the value is an index, but that's how dfont.rb originally defined it. The difference is that dfont.rb supports specifying fonts by both name and index. I'll rework this so that it supports name look ups as well, to mimic the dfont implementation.

[pointlessone]

You can get a proper map by including Enumerable into Collection.

[jamis]

Excellent point. I've updated both PR's.

[pointlessone]

@jamis I rebased, squashed and merged this PR. I will close it now. Thank you for your contribution.